As far as pilot certification/experience for those 25sm sightseeing flights, the FAR's generally require only that the pilot have a Commercial Pilot certificate with appropriate category/class ratings, which in some circumstances one can earn with as little as 190 hours for Airplanes, but usually at least 250 hours. However, there's a lot more to it, including that the pilot must be in an approved drug testing program, which is why most flight schools/FBO's without Part 135 charter operations don't do this any more. See the regs cited above as well as 14 CFR 135.1(a)(5).
BTW, that 500 hour minimum for charity flights applies only to Private Pilots; CP's can do them with no minimum hours beyond that needed to get the CPL.