I never sand a car down to bare metal do to heat and not being able to see what was sanded or fixed before. I always used paint stripper and a razor scraper on exterior metal. Once down to the red oxide then put a coat of paint stripper on it and steel wool it the rest of the way.. Always tape the gaps so the paint stripper does not go into the jams unless your painting them. Then you only have to sand the edges. Using this method you can see all the original untouched metal. Yes the stripper removes body work too. I then use fine Crushed glass to do from the doors down and the front clip.