as far as your gun goes... you can spray basically whatever you want through it depending on your tip size. I use a 1.7 tip for primer, and a 1.3 or 1.4 for base/clear/special fx. cleaning your gun is key.

as far as paint system used... if I were doing my first paint job today, I'd want to do a base/clear 2 stage. its nearly impossible to fix runs/sags/and other defects in a single stage paint. with a 2 stage, it will be a little more forgiving. If your stepdad "aquired" this gun, I would assume he has a little paint experience. ask someone you know to give you pointers for shooting. and do a few practice runs on something thats not a car. i.e. garage walls, fridges, toilet seats, etc.

compressors... I had a 5hp 29 gallon sears compressor that would not keep up with me for spraying a motorcycle tank last summer. the key to compressors is getting a 2-stage motor. it can produce more air and has a better chance of keeping up with your painting. I recently bought a 10hp 120 gallon comp. That is probably way to big for what you're doing, but I never have to worry about running out of air again. with compressors, get as much as you can for your price range. you can always find a use for more air.

Be sure to get some kind of water filter for your comp. when they run for extended periods of time ( like a complete paint job ) heat from the motor will cuase a lot of water to get into your lines. few things can ruin a good paint job like water in your lines.

good luck

Jason