If it were mine to do, I would clean and sand all of the bare metal back to shiney bright. Use whatever abrasives you wish. I would open the drain holes from the inside. and make sure there is no debris.Then thoroughly wash the original paint job, being sure to remove all the wax. Next sand everything down to smooth with 400 grit,
The best/easiest paints are 2k. Excepting the primer, these are true "epoxy" 2 part aerosol paints in rattle cans. There is a button on the bottom of the can which activates the paint. I'm just guessing but you might need 2 cans of primer, 2 cans of paint, and two cans of clear coat.
You can get 2K from Eastwood, but each can will cost an additional $10.00 to ship. NAPA also sells them, no charge for shipping. One NAPA store here in town, has a paint specialist who will mix the paint according to the paint number (not the VIN) and also eyeball/correct any subtle differences between the new paint and the old. Eastwood can't do this, of course.
The first pass is primer. This is a 2K that dries by evaporation. It's good stuff: good coverage, good texture, good body, and fast drying. Spray on 2-3 coats in long strokes with a 50% overlap, each right after the previous flashes off.
Wait 12 hours, then sand again with 400 grit but only if imperfections are there.
Then apply 3 coats of 2k paint, long straight strokes with 50% overlap. Sand again if need be, but use 1,000 or 2,000 grit to smooth off any drips or dry spots.
Then spray 3 coats of clear. If need be, wait 12 hours, then wet sand with 2, 3, or even 5000 grit.
You probably won't need to sand in between all those coats, but if you want perfection and you do not have a spray booth, you might encounter some problems.
Then buff with a polishing compound for a showroom shine. This is time consuming and expensive, but the very best way to go. Done right, that final finish, the fine wet sand, and the buff job, can look every bit as good as a professional job, perhaps even better with a 5,000 grit wet sand and buff.
Here's a rattlecan tailgate I did for a friend. Note my reflection. Caution! Images in the tail gate appear fatter than they do in real life!