I've painted a few of my cars, and about a gazillion sets of race motorcycle bodywork over the past few years, and did an article for Roadracing World magaizine on DIY painting. I'm about to crap in the punchbowl here, so please understand that I do truly have your best interests in mind here:
"Essentially every clearcoat system available today is a catalyzed urethane. There is no approved filter-type respirator for these materials. The only safe way to use these is through the use of a supplied-air system. Failure to do so is to subject one's self to isocyanates which are particularly nasty neurotoxins"
I've done a few things in basecoat/urethane clear so long as they're small and I can work outdoors where vapors dissipate quickly, and I can stay upwind, still, it's genuinely bad stuff, and you can't fix what it does to you.
I recommend the use of acrylic enamels. They're getting harder and harder to find, but PPG Omni works fine, and an acrylic clear is available.
I shot my Sprite with the last of my Speedwell Blue PPG Delstar last fall, and it'll be a sad day when the last of my stash of Delstar is all gone...
Done correctly, acrylic enamels (which use a hardener and a temperature-specific reducer) lay out very well and can be colorsanded, cut and buffed to a mirror finish.
Mainly, as others have stated, it's literally 97% preparation. My Sprite was 2 years of restoring the tub, getting it all straight, priming, blocking, priming , blocking etc. etc. Shooting the paint took about 2 hours, and it was a day to wet sand and a day to buff.