I would rub it down using a long block,like 18''till you can just see base showing tru. then reprime
and guide coat it and rub again with long block .
Is that crazing in old paint? if so rub it till it's clear.or it will break thru down the line.
240-320 dry rub before priming,after priming 320-400 grit.
I like dry rub.no water toblow out when you paint.
first coat I'd use a epoxy primer.it sticks well.then regular hibuild primer.
if you need to rub the epoxy,dont leave it too long as it dries very hard.
how far are you taking it? are you top coating too?