I called the Virginia DMV this morning and was ASTONISHED at the good service provided by Shelly, the nice lady there. I quoted her the laws and told her what I thought they meant, and she responded with "You're absolutely right." First it was nice that I was right, but it was REALLY WONDERFUL that I got a set of straight, unequivocal answers. Yay for her!
Not trying to be a lawyer: just reporting what I read, what I said, and how she responded to my statements.
1) In Virginia, a bus (>15 passengers) is a commercial vehicle, EXCEPT when operated by an individual solely for his personal purposes, such as recreational activities. So I won't need a commercial license. VA Code 46.2-341.4
2) Airbrake endorsements are for commercial licenses in VA, so not needed.
3) ONLY a schoolbus can 1) be yellow, 2) have safety lights and stopsign, and 3) be labeled as a school bus in 8" black letters. The key word is "And" - if I knock out the safety lights, sign OR paint over the "School Bus" part, I can drive it yellow if I want. VA Code section 46.2-1089. I sent my wife some photos of psychedelic paint jobs (see Google Images for Hippie Bus) and she said "No. Just No." Ah, well.
Also, called State Farm and they nice lady there said she wrote a policy for a tour bus conversion recently, for comp and collision as well as liability, for about $400 a year. She said she wrote it as a personal vehicle because RV policies are lots more expensive (and she was able to do that even though it was titled as a motorhome).
Progress!