DYC sells their "basic" kit with 3 gallons. I've never done an entire car but I think that's what I'd go with. The gallons aren't that expensive.
Mr. Furgal --- Part of the beauty of PlastiDip is that it needs very little (if any) prep. Clean the surface, make sure any loose paint is gone and spray. Also, it's very forgiving. With paint, it's easy to get runs, splotches, etc (I'm not a painter so I don't know all the terms for "jacked up paint"
). With PD, you almost can't go wrong. If you have a problem (a seam is showing or you get a run), just spray another coat or 2 and it generally disappears.
I would never consider painting my own car. I've never done it and I just don't have that kind of talent. I WOULD PD my own car (and plan to eventually).