I have discovered that sanding tooling gelcoat is a pain in the yeah... but fine polishing is something it takes really well.
So what I am looking for is a quick and easy way to go from printed part to a good enough finish on the plug, that when I make the mold I just have to hit it with some polishing.
In my mind the easiest thing would be to use a combination of sanding and spray filler of some sort.
I do happen do have a shitty miniature spray gun with a 0.8mm nozzle but I would prefer a fast drying solvent free canned filler.

So do people have any advice on solvent free canned fillers for people not equipped to spray 2k stuff?
And what would be the recommended fillers for 2k stuff?
And also would solvents in fillers/primers/paints attack a sprayed PVA release agent?
And would you be able to go strait to polishing when using PVA as a release agent?

Or what is you personal favorite method to go from 3d print to plug to finished mold?

Don't use filler cans. You will get problems with the mould almost guaranteed. You could simply use coating epoxy.