Just when I think I know what I'm talking about and answer a question like this, I find out how much I don't know when other more experienced folks chime in.
I think I know the answer, but take it with the "sort of still newbie, backyard hack" disclaimer.
If you've put down good coats of epoxy on areas that will not be seen, or the goal is just preservation and/or OEM style appearance for inner panels, and the color/sheen is what you want, then you are done.
Sealer (which is usually reduced epoxy) is for a last coat over prior (cured) epoxy or filler/2K primer/exposed bare metal/poly primer. It "seals" all that stuff before you apply single stage or base coat paint. This provides a great, uniform material for the next stage, with great chemical and mechanical adhesion to both what it is sprayed over, and for the material sprayed on it.
If shooting over cured epoxy, or 2K that is more than a few says old, then that needs to be scuffed before shooting sealer.
I think that is right, but others may offer better advice.