I am not a painter, but I work with a painter (and have hired professional painters) who all follow the procedures below.
Read the instruction sheets that should be provided with the paint (these sheets must be available/provided, or use another paint line)
If you have clean (blasted) metal, you can/should spray epoxy primer over the metal. There is no need for etch BUT
wipe/prep the metal as described by the paint manufacturer (you can wipe with lacquer thinner, but carefully/thoroughly wipe off the thinner residue with a good quality (and recommended brand) of wax and grease remover. We use one-time-use, non-colored towels for cleaning/wiping.
If you do use self-etching primer, check the instructions regarding the need for an overcoat (like epoxy primer) in order to prevent rust.
Body filler, sealer, and surfacer can safely be applied over the epoxy primer (read the manufacturer's instruction/information sheets, to be safe about this).
All epoxy primers (that we have used) provide information sheets on how to scuff/treat the epoxy-primered surface after different periods of time.
