You can never have enough air! I would think at least a 5 hp or a 7.5 a 10 horse would be the real deal. Don't even bother with the pancake, my Sata gun would drain that thing in about 5 seconds. It can be done with a smaller compressor, but you have to find the right gun for the amount of SCFM the compressor will put out. Don't worry about the pressure too much as most decent guns will spray okay with only about 40-50 PSI. The main thing needed is air flow, not pressure! If you decide to spray most coatings require at least 10 - 20 CFM.
Having to purchase a new setup so you can spray is a decision only you can make. In addition to the gun, compressor, fittings and couplers, you would also need a decent water separator setup at least 25 feet from the compressor so the air can cool down and the separator can do its job.
The good thing is once you have a setup like this you can use it for all kinds of projects.
My .02
Oh and I agree with Rich that a good sprayed paint job can't be beat!
