I have a little experience in this, (not a lot), the only thing I'd add is that 600 is too rough for anything you're doing on auto paint. I started a thread once when a friend gave me an old Mercedes-Benz with REALLY bad paint.
He'd gotten ripped-off on some body work and the hood looked like it was painted w a brush and a nappy roller. The trunk and roof had profound scratches in the clear coat from boxes being stored on it and dragged across, etc. Since I had nothing to lose, I just got some sand paper and soapy water and went at it. Came out pretty good, I think nothing of taking sandpaper to a car now as part of normal detail job. But not 600.
Here was that thread:
http://forums.pelicanparts.com/off-topic-discussions/621306-adventures-auto-detailing.html