I took my GY3 Challenger all the way to the metal when I redid it. I used PPG DP90LF on the bare metal after DA'ing it with 80 and cleaning it till nothing else would wipe off. Let that sit a few weeks, and then scuffed up the few places needing filler....and put the filler over the DP. After that, I sanded the whole car and shot it with PPG K38 primer. I did a few coats of the K38 along with guide coat till it was straight. Then I took it to the painter and said "Here...it's your turn!" I also used PPG base/clear on it. All the paint, from metal to done was about $1500. It looks as good today as it did 5 years ago when it was painted. Use some good epoxy primer of some kind on the bare metal. Some prefer etch primer under the epoxy. I have one car done with etch primer first, and the car above done just with epoxy. No problems with either paint job, so it's probably just a matter of preference. Good luck.