Ok! Thanks all!
Sooo...my plan now is to wash and lightly sand bus just to scratch it a bit. Treat the rust spots with extra love (more sanding, Rustoleum "Stops Rust" spray). Tape off windows, etc. Spray Rustoleum "Primer Surfacer" in light grey (oil based; all I can find this stuff in is light grey and grey). Spray Rustoleum "Farm and Implement Oil Paint" (slightly thinned maybe 15-20%; skipping the hardener) in International Harvester White. We'll see how coverage goes and may apply an extra coat.
If you guys have any helpful tips, or think I should be doing something differently here, please feel free to share! I very much appreciate it!
Now, let's hope for a day with no wind...