im doing a bonnet at the moment that sounds far worse. Ive paint stripped it and was still left with two coats of some nasty shit underneath. One is black, the other dark maroon. standing on it with 36grit even struggled to get that crap off! anyways came down to 80 then 120 and was still left with some nice big rust pits. Rust killed the lot and sanded excess rust kill off with 120 again. Then hit it with 2 fairly light coats of 1K etch and now im gonna bomb 2K spray putter over the etch.

Your rust sounds pretty superficial. Id just hit it with 80-150 on a grinder/buff pad, then etch the lot and then spray putty and block it back before primer.

Ive heard that 2k primer has incredible bonding qualities and is good to use on bodgy rust repairs straight after rust kill. So grind back, rust kill, 2k primer > then bog, spray putty and then prime.

Also you might want to give 2K a go even if its in your shed. far less prep required (ie paint straight over 320) and tonnes less buffing. I know the finish isnt ridgy didge old skool but its far less work and believe it or not... the 2k ive been quoted is almost 1/3 the price of acryilc!