What would you like to be able to do?
Depending on what your plans may be, various air tools consume air by CFM, and if you choose tools that consume a lot, get a compressor that is up to the task. Otherwise your "quality time" with your car will be squandered as you wait for your undersized compressor to "catch up".
Using tools are to get tasks done faster. If you are waiting on your compressor all the time, you may as well use hand tools.
Smaller CFM output compressors are for smaller tools, mainly for intermittent use. Larger CFM output allows the use of more types of tools, including sanders, DA sanders, paint guns and the like.
I have had an undersized compressor for over 10 years, bought new. Too small for most jobs I ENDED UP needing to do; just wishful thinking, I had to pass.
My next compressor will be over 10 CFM capacity with a 60-gallon tank- and aside from sandblasting ships in drydock, I will be OK. For automotive, there is such a thing as "NOT ENOUGH" and "TOO MUCH"- it's difficult to do fine feather paint sanding on a fender with a horse of a "bull grinder" that would like to snap both of your wrists when you hit the trigger.
My advice, for what it's worth- consider the CFM rating of the tools, THEN look for the compressor. The compressor will take up room-make sure it gets full use and not wind up just being something that is in your way.

Cheers!

snapped_bolt

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'81 240D For now, a good place to borrow new parts
'80 300TD Probably will be put back into service!
'79 240D BACK IN SERVICE SINCE 09/16; limited use, oil leak. Guide pin r/sealed/replaced. Still a leak. Front crank seal....