Just like everyone said... Double action unit, buy a compressor and moisture trap, practice, practice, practice. I have a Badger Crescendo also, love it. I recently bought an Aztek, not so fond of it.
I still do most body color with spray cans. Airbrushing will open new opportunities such as fades, flames and most important, Alclad metal paints. Theres also little things like doing black window trims and such, when you really don't want the volume a can puts out. Touch-ups on body paint become easier also, because you can decant the paint from the can and shoot it thru the airbrush.