Shop air dilemma
I see some good advice above but the "King" of compressor specs for blasting has only been casually hinted at a few times-
CFM, CFM, CFM.
CFM is the king, almost nothing else.
Gallon capacity can be zero. PSI can be 75.
HP does factor, but again-
CFM, CFM. CF'n M!
I'd advise to get the highest CFM@90 240V unit you can afford.
...and I'd also advise at least 15-20 CFM@90.
Usually it will be a 5HP or more motor, and a 60-80 gal tank.
Don't shy away from a smaller tank. The CFM will more than make up for it.