I have several air compressors. the bigger the better. for what you are describing, you should be fine with a 30 gallon unit. but look for one with an oil filled compressor. also, look at the motor and VERIFY that it will handle 240v. some motors say on the data plate 110/240... but the posts to rewire for 240 are not present. (ask how I know...) a 240 motor starts WAAAAAAY easier! (my current 110v motor will kill all the lights in the shop when it starts...) My Mercury vapor stall lights take SOOOO long to restart after they drop out from the pump coming on.
if you plan on doing any body/painting work, you will need a good dewatering system. if you plan on using an impact gun for more than tires, 30 gallon is going to run the compressor ALL THE TIME... move up to a 90 gallon tank.
if you go with a used tank look it over carefully. I got one, and there were pinholes all over it. water does a number on a steel tank! what ever tank you choose, remove the petcock that comes with it, and install some brass pipe and a real ball valve where you can reach it to drain the water that collects in the tank.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!