For and blasting, I'll lend my experience.
I've got an oil less, two stage, 3.5 horse, 25 gallon, porter cable air compressor that does 5.1 CFM @90 PSI.
I've been sandblasting, using the harbor freight cabinet (the larger one) and I've been able to do valve cover size parts or larger.
However...
CFM makes all the difference and tank size helps you go longer. At 90psi I can do a large valve cover in a five minutes. The problem is that my air compressor cannot maintain 90psi for 5 Mounties, it can do it for maybe 1-2 minutes and then it slowly drops the psi to around 30. At 30 psi I can still sandblast but now instead of being able to do a whole valve cover in 5 minutes, I can do a 5"x15" section in five minutes.
However...
I was not always able to do any sand blasting once my compressor got below 45psi UNTIL I upgraded to high flow fittings. The high flow fittings have me a huge increase in performance, not only with my sandblasting but also with my harbor freight short nosed impact gun (earthquake xt or something).
Ideally I would want a two stage compressor with an 80 gallon tank, and a cfm rating as close to 20 @ 90psi as possible for the best results as a hobbyist. In order to get that performance though, you would not only have to spend $800-1400, you would also need to have a 240v receptacle available to plug it in to (lucky for me, I was capable of doing that myself and saved around $500-1000 for an electrician).
Anyway, that's my two cents.