I currently use a 0.5 gallon tank and it's too small. I'd like to apply a base coat to a 1/35 AFV without having my compressor start during the painting session. How big should the air tank be? I know that the bigger, the better. But I wouldn't want to end up with waiting for a long time for the tank to be filled.

Okay where's the rocket scientist ? It all depends on what you want your compressor to do . If you want to be able to run air tools , such as drills and nailers you need a large tank , the are CFM hungry and a regulator that will go up to 100 plus pressure . I would say ten gallons but then your compressor has to have the capacity to fill real quick . And they tend to be noisy . I would also say stay away from the oiless compressors they don't last as long . You could visit Harbor Freight if there's a one near you and check out the air compressors and storage tanks .

Buy a can of compressed air. Guaranteed no noise and it should last you for several sessions.

But the compressed air can becomes weak as the air supply runs out .

Use an over-inflated spare tire. That was my first "compressor."