Well, ummmmm...
Lotsa questions in this one.
Single stage is all you need. Two stage compressors are designed to run at higher pressures. You pay more for that. A single stage will normally pressurize up to 125 PSI. You will normally use 90 PSI or less, but PSI isn't your yardstick here. CFM at 90 PSI is. Check all the units you compare to get the most CFM at 90 PSI.
The air capacity is your other measure of importance. The capacity will allow your motor to cycle less.
Another factor is the motor/compressor design. All have benefits and drawbacks.
I prefer a belt driven compressor. Reason being, if one part fails you can replace it. This is why I bought a Craftsman. Sears sells ALL replacement parts and will ship them to you.
When it comes to compressor units, an aluminum "jugged" steel SLEEVED unit will serve you well. It is made for the demanding non commercial user. The aluminum dissapates the heat nicely and the steel sleeve stands up to the wear and tear of rigorous use.
I have a 5 hp, 60 Gallon, 9 CFM@90 PSI sears Craftsman Single Stage unit. It works very well and I found it on clearance for $260!!!
Woo Hoo!

CJ