Guys my first post of many here so get ready to answer a ton of rookie questions in the near future. I have scrolled through the search option but didn't find much on what Im looking for. My 93 trunk Mustang had peeling clearcoat. Looks as if she had a cheapo paintjob in the past and the prep wasn't taken seriously. What I have done thus far is take a DA with 80grit and carefully take off the clear until I got down to the base/old primer while trying not to get to bare metal. I did get bare metal in a few small spots but covered them with some aerosol (Rustoleum} etching primer. After running the 80grit over it I then switched over to 220grit. I have bought new fenders, trunk lid, and fiberglass cowl hood, to get away from as much body work as possible. The front and rear bumper covers are immaculate so it's just a matter of scuffing them up and spraying. I'm not looking for a show car paintjob but want it to look decent. My plan is to do all of the body work and have someone else actually paint the car. Enough rambling and on to my questions...

1. After getting her sanded down to the old base/primer what would be the best primer to spray directly over what I have? Epoxy, Urethane, 2k, Polyester, High Build?
2. What grit sandpaper would be best to prep with before the primer to get the best bond?

Use epoxy primer, it's a good sealer and gives the best adhesion.
I would final sand it with 400 to 600 grit.

I have a nose panel that I have sanded down with 180 grit, filled in some pin holes with puddy, resanded with 180, 320, and actually wet sanded with 400. Now, everything is smooth, but I think there are some bare spots. Do I cover the entire nose panel (metal) with epoxy, then a 2K high build primer, wet sand with 600 and then it should be ready for base color?

I would cover it all, mainly because front end parts will get a lot less
road rash (chips) if primed with epoxy first.
I now do all my bumpers with epoxy and have seen a huge difference in
them getting less chips.

No need to put 2k over the epoxy unless you need more filling to
sand smooth. High end resto shops will cover the 2K with epoxy
when done. Not the other way around.
Epoxy is the best sealer for painting over.

Most epoxy primers don't have to be sanded if painted over
in less than 24 hrs, some up to a week.
I still like to sand mine with 600 before painting just to
get it real smooth.
It sands much easier when cured for 48 hrs or longer.

I don't mean to high jack the thread and I have my own going....I did the engine bay in 2k epoxy and it came out looking great! Now, I am just going to shoot some single stage paint over it and be done!

Now for the nose panel/bumpers....I sprayed the nose panel with 2k epoxy, but I ended up using the SEM flexible high build primer instead of the 2k urethane primer....should that cause any issues? Since I'm spraying metallic silver, I plan to fix remaining imperfections, respray another coat of high build primer, sand with 600, then paint. Do you recommend I go and get another can of epoxy primer and spray over it just before paint?

It's a judgment call, I don't know if I would buy
more epoxy to paint it, but I definitely would use it if I
already had some. It will reduce road rash.
All it takes is a sealer coat of epoxy.
(that's a epoxy coat reduced 50/50)
And you can spray over it in a couple of hours.
But it's your call.