first of all, don't go back to bare metal, unless you want the job to take ages
all you need is a few sheets of 800 wet and dry paper, scotchbrite, and this stuff called scuff stuff, ring an auto supplies place for all of it, shouldn't cost much
then just rub everything with the paper, and then go over everything with the scotchbrite and scuff stuff, to make sure everywhere you are painting is dull, so the paint sticks
are you going to hi-fill the dents?
there's no point putting heaps of coats of paint on, just more chance of a run, just make sure the painter knows what he is doing and it will look fat