Don't need etch primer with epoxy primer. and the last thing you want to do if using etch primer is put to much on, one thin coat is plenty. I would fix the rust out areas before taking the rest of the paint off. Not sure how much filler you are going to need but if it is a deep area use 36 grit before filler, 80 grit for shallow areas. Bare metal no epoxy or etch primer just use filler "bondo" on bare metal. Don't use cheep filler "bondo" Ever coat is good about $80 a gallon. cheep would be $30 a gallon and cheep filler you will work hard to sand it.
