Now wait a minute. This is the plane you bought after asking us for "a cheap way to build retract time" wasn't it?
Let me throw a couple of suggestions out there. If you still want that Twin Bonanza sometime in the next decade, you probably don't want to be dropping big money on a panel right now. OTOH, if you've decided the Bo is gonna stay, then you probably wan't something nice.
First off: I wouldn't bother with an IFD navigator. Their main advantage is that they're slide-in replacements for the Garmin GNS series. You won't be able to get that advantage, so IMO you're better off sticking with Garmin. You mention not liking the flow in "the GNX and G1000" - I'm going to assume you meant GNS and G1000, as they're pretty much identical in how they work. Good news: You can't get a G1000 in your plane, and nobody in their right mind would be recommending GNS series navigators now, they were discontinued 14 years ago! The Garmin GTN and all of their modern stuff works in a completely different way - Just a main menu with icons instead of the GNS/G1000 groups and pages.
For the "go all out" version, I'd do this:
* G3X Touch 10" with EIS - Putting in a 7" on the other side would be optional, more on that in a moment.
* GTN: You could get a 750Xi and use it kind of like an MFD, or you could get a 650Xi and the 7" MFD. Or a 750Xi and the 7" MFD if you really like lots of big color screens and hate money like I do.

* GFC 500 autopilot with pitch trim and yaw damper. Your pax will thank you for the yaw damper - Beeches are happy airplanes, they love to wag their tails!
* GTX345 transponder. If you really want a backup GPS, you could do the GNX375, or you could get a GNC355 as your second Com radio.
* GTR205 #2 com radio
* GMA350c audio panel if you want to talk to the plane, or PS Engineering PMA450B otherwise.
Now, to accomplish all of your goals while also at least attempting to not have the panel be worth more than the rest of the plane and maintaining the classic look:
* GI 275 AI: This gives you primary instrument capability for your entire six-pack. I'd still keep 4/6 but if you have one of them go bad this will keep you from being grounded.
* GI 275 HSI: Gets rid of the wonky DG and gives you a lot of capability, also functions as the backup for the AI. With two of them like this, you can ditch the vacuum system and get some useful load back.
* GNX 375: This would replace the 300XL *and* get you reliable ADS-B
* GNC 215 Nav/Com 1
* PS Engineering PAR 200B audio panel/Com2
* EI CGR-30P engine monitor - This will allow you to use the existing wiring and probes that you have for EGT/CHT most likely. I didn't see mention of what model your current one is or a picture, just that it's an EI, so check on this to be sure.
* Keep the S-TEC
You can - It can be on the side of the PFD.