Im curious, how big (gallon wise) of an air compressor do you need to paint a car body? Ive seen pics on here with people painting there 3rd gen in there garage. Ive been wanting to get one... Would anybody know? thanks!

25-30 gal
what you need is a good size tank or fast compressor to hold it at the pre-set PSI

Really just get the most air you can afford and you should be pretty happy. I would say 80 gallon i know that sounds huge but it is so worth it if you buy a quality compressor. I had a 60 gallon single stage and it just couldn't keep up with anything and i spent over $500 on the damn thing. I now have a 2 stage porter cable C7750 and it rocks! pretty reasonable on amazon too. Really for painting a car with all the sanding and the amount of air that air tools now seem to demand i would go with a good two stage pump and about an 80 gallon tank. you could probably get away with a 60 gallon if you wanted to do the work all by yourself with out help. which by the way sucks. The bigger the better

Also CFM rating is very important. You need a compressor that rated AT LEAST the minimum CFM requirement by the paint gun. For example, my paint gun DeVilbiss requires 12.5 CFM @ 23PSI, and my compressor is rated 15 CFM @45 PSI (the lower PSI, the higher CFM). you can get by a small compressor, but you have to wait for the compressor to fill up.
do not forget to buy a water/ oil filter

I own a bodyshop and we use a 7.5 hp 28 cfm @175psi 80 gal unit. You don't need one that big to paint a car. When I started out I had a 3.5hp 30 gal sears air comp that did the job just find as long as I made sure the inlet filters were clean and one tool at a time was used. That one cost me $160.