The only way to go for any serious auto body repair is at least a 5hp 2 stage compressor. The hp and tank size are not a great way of judging the air supply. I sold air compressors for 8 years so i seen alot people worried about tank size. The most important spec is the cfm rating at 90 psi (for air tools), dont confuse this with the "free air cfm delivery". For sandblasting and heavy DA use you want a minimum of 17-18 cfm at 90psi. And that would be for your average pressure blaster use (80-90lb capacity, 1/2 id. sand hose 3/32 orifice nozzle). Tank size on these compressors are usually 60 or 80 gallon doesnt matter, the cfm rating is product of the pump itself. The larger tank will give you more reserve air.For minimum home type restoration you can get by with a 5-6.5 hp single stage compressor they usaully give about 9cfm at 90psi, They will work but give you less power for impacts, and will run almost constantly with a DA sander. They will work but due to running almost constant you may go through a pump a little faster then you may like,(if you blast alot) but it will get you by. Definitely stay away from oiless direct drive compressors, They will not hold up.. Sorry for the long winded answer but just thought i would try to help.
Oh by the way a quick rule of thumb, If the air tool uses 6cfm you would like to have at least 12 cfm to run efficiently.