I did it! I picked up a 2004 Chevy Express 3500 gas 6.0L with 172k miles for $3800 with as little rust as one could hope for on the east coast. This one was aging out and was maintained regularly as a fleet vehicle under pretty attentive care, seemingly.
Pics for now on the ad that hasn't been taken down yet, because I can't access this site very well from my cell phone. Will post my own in the next few days!
For now I made a to-scale drawing of the bus itself and am moving around pieces of construction paper so I can envision the layout. I swear, I'll probably end up making a diorama.
Tactile learners dream with their hands!
It has 6 windows, giving me almost 15 1/2 feet to play with behind the driver's seat!
Seeing as I enjoy facilitating and undertaking lots of projects, I want to retain some space for hauling things or raw materials in the bus itself-- firewood, bicycles, cool trash. I'm thinking of building out a "trunk" in the rear, accessible by way of the emergency exit, or factoring that in to my passenger seating area up front (bench seats? van seats? arm chairs bolted down with belts?).
Anyway, I'm looking forward to keeping y'all up to date on things. Thanks for bearing with all the questions so far-- I promise there'll be more.