Dan,
I'm sure you've heard it before, get the very biggest you can afford. I recently bought a two stage, 80 gallon, 18 cfm at 100psi, 20 at 175, and it does what I need. It has a built in regulator so you can turn down the pressure to the tools being used. I run my sand blast cabinet, impacts, 10 gallon sand blaster and it kicks in frequently when using high demand tools like the cabinet and blaster. It doesn't run very long though. I hope this helps.
