What kind of compressor do you have? If it's undersized, it may not keep up if you're planning to spray the whole car. There's nothing wrong with doing it one panel at a time though.
I'm not sure off the top off my head. It's one of the Husky compressors that stand about 4ft tall. I'd say it's probably a 20gal? I also have an old school home made one that my grandpa made down on the railroad that's probably even better at 30gal or so.
If I do it, i'll probably do the separate panels two at a time at first and then finish the roof/quarters at the end in one swoop. Think I'll have enough compressor for that?