First is etch primer to seal the metal from moisture.
Some say to put filler on bare metal but really it's fine to put on etch and primers as long as you have keyed the area to be fillered.
I've never put filler on bare metal cause filler is a sponge for moisture, if you wet rub the panel there will be moisture trapped and effectively rust out the panel.
I only dry sand filler and primers until the sealer coat, epoxy, is fully covered on the car.
Seam sealer can go on bare or primer, your only sealing gaps up, the seam sealer can be painted over.
As long as you've scratched up the area to be painted, you can go past etch and use epoxy over bare metal to seal the metal from rusting and filler on the primer. Did this on my blue van 10yrs ago and hasn't broken out in blisters or paint falling off..
This is going to cause arguments on how and what etc.
Etch is cheaper than epoxy and can be welded thru where as epoxy can't be welded thru. If I get the car grit blasted I always etch it asap then I can relax on working on it.