Rust removal, how far????

There are several chemical rust removers but sandblasting is the best way, it gets it all and leaves the metal etched for the primer. Sandblast the jambs, corners, crevices, braces and the strong portions but don't sandblast the outer sheet metal without testing how to do it on a scrap fender or door, you can easily warp sheet metal. I turn the air pressure way down to do the sheet metal. Also strip the paint before you sand blast the sheet metal, a lot less chance of warpage, sandblasting will get it but why take chances.

As far as primer, epoxy is far superior to etching primer. Etching primer was the way to go 20 years ago but it is old technology and there is no comparison when it comes to durability and sealing the metal from the elements.