Strip it all the way to the metal! Last one I did, I used some sanding discs for a 4" grinder. They look like a scuff pad, but they're stiff. I got them at Lowes, and it takes about one per panel. They were $7 each at the time, but may be a little more now. They won't heat the metal up and warp it like sanding discs on a big grinder. You could use Aircraft Stripper, but if you don't get it all off the car when you're done....it can ruin your new paint later. Use epoxy primer on the bare metal after you clean it with wax and grease remover, and do any filler work OVER the epoxy primer. Use a good 2K primer for all your blocking. Alternating between dark gray and light gray primer between sanding will help define low and high spots. If you decide to paint it yourself, practice on an old hood or something before you tackle the base clear. There's a lot of educational painting videos on You Tube. Good luck....and kudos to you for not being afraid to tackle it yourself!
