A few auto body questions

I got a few questions sorry if I get long winded but here goes. I got a 72 Scamp im doing body work on my own and have very little experience.

First question. Im stripping down with 50grit discs. The top coat was flaking severly and after getting that off im down into the factory primer and bare metal in some areas. What grit should I go back over? Can I follow the 50 grit up with a 180 then epoxy? Or should I follow it up with something else?

Next question is I dont plan to go all they way to bare metal. I really like what im seeing with the original primer or what ever it is under the factory top coat. Nice and smooth no cracks or chips in it. Is it ok to not go to bare metal and follow up with the above method?

Also how can I be darn sure that none of the underneith is Laqure finish as most finishes now arent compatable with that?


Last question is paint gun. Id like something a little better then the cheap $10 harbor freight gun i used for the engine bay. I see they have a little better one for $34. or can yall recommend a good ECONOMY gun? Even a good used one would be ok.