That is what is thinking. If I try to fix one spot it might pop up somewhere esle, because of the bad paint. I'm not wanting that.
So take it down to bare metal. I read something about using a sealer. Should that be done after primer? Just before painting? Or before primer?
It depends on the paint system you use, but typically some primers are direct to metal and some are not thus requiring an etch/wash primer before the primer goes on. Some epoxy primers can be used as a primer or sealer being called primer/sealers depending upon reduction ratios. Some epoxies are also not direct to metal requiring an etch primer. Epoxies typically don't fill or sand well.
Once you get all your bodywork, priming, and prep done you use a sealer before applying color. You can use epoxy sealer here again but most paint systems have their own product for this and many paint systems REQUIRE this sealer before spraying color/topcoat. This assures uniform color across the vehicle. Many modern single stage and basecoats are translucent so if you don't seal it prior to putting on color you'll be forever with multiple coats trying to cover primer spots and sanding cut throughs etc and many paint systems call for a color coded or tinted sealer. The sealers also typically have adhesion benefits. Cheaper paint has even less pigment per volume.
In the restoration world stripped panels usually get epoxied and then bodyworked and reprimed with a 2k high build over that. When working at a Gm dealer doing warranty delamination jobs we used to strip the panels , prep the rest, roll them into the booth, epoxy the bare panels, flash time, sealer, flash time, and then paint wet on wet.
1. Strip to metal
2. Etch prime then prime or DTM/direct to metal primer. Usually some type of 2k high build primer if over bodywork.
3. The beginning of the paint process seal it with the appropriate tinted/color coded sealer. These are non sanding type sealers. Paintable after the flash time with basecoat/clearcoat or whatever you picked out.
The technical data sheets (TDS) for whatever paint system you choose will have all the info you need and most are available online these days.