Interesting timing... Karen is considering many of the things you're asking about...
Okay, first things first...
Concealed Carry is a lifestyle change. It's also a gut check of your opinions on a lot of things, life, death, etc. It's not to be taken lightly. Only you can decide if you are trained, and able, to wield deadly force. You also know from your class that there are far more situations where deadly force is not required than when it is.
Think hard about it. Can you decide NOT to shoot? And can you decide when you MUST shoot?
Enough said.
Knowing that a gun is for concealment, changes the options more drastically than say, buying for home defense.
A couple hundred bucks, even in today's political insanity and panic buying, still gets you a good quality shotgun.
Next up, you're 21. Are you attending a school campus? Have you looked into whether or not you're even allowed to carry where you spend the majority of your daily time? Just checking. Nothing as useless as money spent on a carry gun when you can not carry.
Budget security into your decision. Cars are not secure. How will you feel if your firearm is stolen and used to kill someone? Be responsible. Make sure it's always locked up with quality security gear.
If you have kids around, Ever... Ever... Ever... you MUST secure the firearm completely whenever it's not on your body. A $60 gun lock box is crap for keeping someone from stealing it (they'll just cut the cable with bolt cutters and take the box away somewhere else to break into it later), but if it keeps prying little fingers from handling your gun, it's doing its job. Kids will find firearms wherever you hide them. Do not believe they won't. If you have to, disassemble it and lock up the parts separately.
9mm is a good all-round option for most beginning shooters. It's powerful enough to use for defense and actually stop someone, but doesn't have unmanageable recoil and other things that make you work very hard at learning just to shoot. What's your shooting background? Will this be your first handgun? Fired some rifles and shotguns with family maybe? Handguns are a bit of an art of their own. To really learn what you like in a handgun, you have to shoot them. What feels great in one person's hand, won't necessarily in another's hand.
I recommend spending time and money at first on instruction, range time, and find a range that has a decent rental gun selection, or find folks you know or can get to know who'll let you shoot their stuff. Here's why.
A gun for target shooting at the range doesn't have to be small. It doesn't have to be reliable. It doesn't have to do anything but shoot, and as you get better, it has to be accurate. Almost any handgun in the market is accurate, but many to a novice shooter will seem not to be. Why? Size mostly. Aiming a small pistol is by nature, harder than a big one. The distance between the rear sights and front sights is shorter. But, for concealment, you may have to learn a smaller gun. In fact if you truly get into "EDC" or everyday concealment, you may need to be proficient with and own more than one weapon. What conceals well in a pair of jeans and a t-shirt may not conceal well in a tuxedo. Or running shorts. If you see what I mean.
However, you will be surprised by how big something can be that can be concealed. Lots and lots of folks conceal medium-large guns every day of the week. They've modified their clothing choices and lifestyle accordingly. A firearms instructor I know has two carry guns, a Glock 19 which is almost every day, and a Ruger LCP. He doesn't like or trust the LCP *as much* as his Glock, but sometimes he can't get the Glock concealed.
And that leads to the next point...
You want any concealed weapon to be one that a) you trust explicitly and b) you shoot well. If you shoot a Glock 19 better than say, a baby Glock... You should be carrying the 19. And as far as trust goes, I know folks who won't carry a pistol until they've fired at least 500 rounds through it, often more, so they know every single quirk it has and that it "always goes bang" with their chosen defense rounds. It must be as comfortable for you to use and you must know it well enough as your favorite pocket knife. One handed. In the dark.
Okay, taking some stuff from your posts...
Safeties: Your number one safety is between your ears. If you are not firing the weapon, your finger is off the trigger and outside of the trigger guard, period. Always. If the weapon isn't in your hand it's in a holster that protects the trigger guard completely. If nothing can get in the trigger guard, the weapon can not be fired.
Here's the downside of manual safeties. Take a defensive weapons course if you can afford it. When the human body does an adrenaline dump under stress, the very first thing to go is fine motor skills. Manipulating a safety while making a clean draw and presentation toward a serious enough threat to you to require deadly force, can be difficult, depending on the safety. You must practice. Racking a slide is also often not possible if you've already started shaking. Seriously.
You want simplicity. You draw it, finger off the trigger, with a proper draw, so you don't muzzle yourself or anyone other than the threat, and you squeeze. The vast majority of self-defense draws happen at less than 21'. Further away than that, you can't guarantee deadly force was necessary and you can probably RUN away. You're not a cop, and you're not going to take up a cover position and fire across the street. Just RUN.
Now, even at 21', an attacker can close that gap in 2 seconds. You MUST practice draws from concealment, and firing accurately enough until the threat is neutralized, check the condition of yourself and your weapon, LOOK AROUND to both break the tunnel vision and the shock that you just had to shoot, because 60% of street attacks are by more than one assailant (his buddy is about to hit you from behind with a baseball bat to avenge his brother you just shot), and reholster without looking to keep your eyeballs up and maintain situational awareness.
Sound like a lot of work? It is. If you're going to carry, be serious about it and get defensive pistol training. Do you know how to clear a weapon malfunction and/or reload your weapon with one hand? (Yes, a semi-auto can be reloaded with one hand and a holster. And racked if it didn't slide-lock.)
So... There's some thoughts. The point you're at now is make sure you know how to shoot. I'd want to put at least five different firearms in your hand at a range and see what you shoot best before recommending a specific one. Rentals are great for this. My range rents 30 different handguns or more, at a cost of $18/hr to non-members. What's your life worth? At today's ammo prices, are you willing to buy a couple of boxes of ammo a month and range time to keep your skills up?
Holsters: You're going to go through a few of them figuring out what works for you. Unfortunately holster makers typically don't take them back, so you'll have a drawer with a few eventually. And again, some work well in some clothes while others work in others. I recommend starting with anything that stays strong-side and not getting too fancy. Cross-body draws are a great way to shoot yourself, and shoulder holsters, ankle holsters, small of the back (SOB) holsters and the like are a bad place to start unless you absolutely must have one for your normal dress. Women are particularly challenged in this regard. Men also... If you show up to the park to go jogging in jeans, a t-shirt, an over shirt untucked, just to conceal, you're not going to like your jog very much. Alternatively, you decide to leave the weapon at home because you don't have the right concealment tools, that will probably be when you end up needing it. If you change up your carry position frequently, you must commit to harder training to draw from each, safely. (Cross body also has the natural disadvantage that any attacker close enough to reach you can completely stop your draw by simply pushing on your crossed arm. Again, get tactics training.)
Okay... Understanding the best gun for you is the one you shoot best, I also like the recommendation of the Smith and Wesson M&P Shield. It's a different design than the rest of the M&P lineup and has gotten excellent reviews for a light, single-stack 9mm. They are also, generally impossible to find right now unless you stumble into a store that just got a ship,EMT or you're willing to pay $200 over MSRP. It's at the top of your price range if you can get it from a store that doesn't price gouge. Big box stores are generally being better about this during the recent buying spree than smaller stores, but it's supply and demand. Shop.
Other good options for a beginning shooter to try, IMHO... Are the regular S&W M&P lineup, Glocks of all sorts but in 9mm because you need to shoot and practice a lot at first, and ammo is cheaper...so it'd be the Glock 19, or... If you find you can shoot it with the short grip, the Glock 26... I don't recommend the 40 cal Glocks to new shooters... They're fine, and identically sized to the 9mm Glock frames, but they're a bit "snappy" with recoil and do require a bit more effort to learn to control. Some folks like the Springfield XD lineup, I haven't warmed up to them yet with one exception, we'll get to that in a minute. Kahr makes decent lower priced stuff, and don't count out "wheel" guns. A revolver often conceals very well, but feels different to shoot. Whatever you shoot the best... still reigns supreme.
Our personal thoughts:
Karen and I joined a range. At their normal range prices, you need to shoot twice a month to recover your monthly dues. You won't recover your initiation fee for two years. So you have to decide for yourself on that one. There's also member discounts on gun rentals, and in their store.
Karen found that her hands need a thin grip. She shoots a Glock 19 very accurately for a beginner and didn't find semi-auto actions overwhelming so she skipped revolvers for now. After reading reviews, and holding a Walther PPS, she knows she wants an M&P Shield, as someone else mentioned. However, she also knows she needs to get trigger time in at the range behind a 9mm and learn to shoot. In order to stay in the same "family", she's starting with a S&W M&P 9mm Compact. It's thicker than the Shield, and because its a compact, she knows she will have to put in the range time to learn to shoot it well. When we find a darn Shield, we'll buy it and see if she shoots it well. Luckily, demand is high on them so if not, we'll just sell it off.
Me, I spent a lot of time shooting 1911 models as a kid, but wanted something "tupperware" for durability and price, and striker-fired. My first choice was a Glock, as I'm a good shot with them, etc. But... I knew I wanted to carry, and while Glocks do conceal well, they stubbornly don't do a single-stack for reduced thickness. The local store put a Springfield XD-S in my hand and, the only way to describe it, and you'll know it when you shoot a few different types of handguns, is that for me... It fit my hand immediately. It's as small as the Shield, but chambered in .45 ACP so it's got some punch in a defensive "stop the threat" scenario. But, it does have a downfall... Low number of rounds. I can live with that, but I know I need some serious range time to get accurate with it and I *MUST* do reload drills. I also picked up two extended 7 round magazines for it, but have already found I'm not as accurate with the gun with those and their extended grips. I'm shooting best with the 5 round magazines.
Frankly, I shoot best TODAY with a borrowed Kimber Custom Carry 1911 in .45 ACP. I'm just not ready to blow $1300 on a carry gun that's going to get beat up. I think I can drill myself to as good a shooting with the XD-S as I am with the Kimber. But if not, my bank account is going to take a beating. All those years of shooting 1911s may mean habits that won't go away easily. We'll see.
Honestly, I'm a dead-eye with my Marlin Model 60 and iron sights... but it just doesn't conceal very well.
I love shooting that thing.
And for a final thoughts... enjoying it is important. If you buy something you hate to shoot, it'll sit on a shelf and collect dust while you do other stuff. Get something that screams, "Lets go to the range!" and shoot the snot out of it. Look up pistol drills online and challenge yourself. Find instructors or trusted people who'll show you defensive pistol as compared to target pistol shooting. Bad guys don't paint bullseyes on their chests and stand still at 7 yards waiting for you to get a sight picture.
Another thing. Find a used 22 pistol. Not for concealing, but for shooting. You can practice 85% of handgun shooting fundamentals on a 22 pistol, and get really good at just shooting, for far far less money than flowing through boxes of 9mm. A half brick of over 500 rounds is $25. Maybe $35 if your gun is picky. That's a lot of basics! Sight picture, trigger control, breath control, practice draws and presentations all the way to firing on the target, reholstering, doing it all with and without a concealment garment, etc. A .22 pistol can let you work on all of that without breaking the bank.
Interesting side note here. If you find you shoot the M&P line of pistols well, S&W makes a .22 pistol. There are also conversion barrels and kits for Glock and some others. Something to keep in mind when shopping. You can feed .22 into your exact carry gun and shoot for pennies and then swap out the barrel and magazine, and go to town with some 9mm.
(Additionally if you get the 40 cal Glock, there are 9mm barrels available for those too.)
I disagree with the SA/DA comments above... You CAN train to shoot a DA revolver from the start, but it requires more effort on the part of the shooter. And many of the striker-fired semi-autos are somewhere inbetween... depending on their trigger reset feel. On many, there's a long take-up similar to a DA and then a place where they tighten up and break like a SA that's already cocked. You can release only to the click, and you're right back at that point where it feels like an SA. Short crisp trigger pull.
Okay, that's enough. Like flying, just go shoot. You'll learn more, faster.
Have fun shopping and shooting. Train and stay safe.