if its not rotten leave it on the car! to pick a rear 1/4 panel off is alot of work. and you cant paint it off the car and then hang it back on. it has to be spot welded back on then painted. putting it back on is achieved either by pooling (making a pool of molten metal on the join) the metal or by use of a proper spot welder. obviously youll have to fix any rot you find before putting it back together....
as for stripping it. paint stripper or a D/A (dual action) sander and gradually go up the grit grades till you have a bare smooth finish. and go from there.
just beware. what lies beneath the paint might not be pretty. its not a job that you cant do at home. but without a fair few tools and good knowledge of cars, body panels and welding. its easier to pay someone to do it

hope that helps.
Jam.