It depends on what your sanding for. Start with getting a board sander that is approximately 16" long for the long flat and moderately curved panels, an orbital for higher speed sanding and then a smaller flexible hand held for corners and contours. Use the 3" sticky backed paper that comes on rolls 50 to 100 ft per roll for the board and smaller flexible and cut to length as needed and sticky backed round for the orbital. Seems like a lot of paper but you will go through a lot on all the different stages of prepping your car for paint. If you want to go to bare metal fairly quickly use a low grit like 40 or 80 to cut it down quickly. If you just want to scuff it for a quick repaint use 320, 400 then 500. If you have body work to do, shape your filler with a 80 grit, then a 180 grit and then move to a 320 before primer. Any bare metal and fill should be covered with an epoxy primer to seal it and then spray your first coat of high build primer without sanding within 3 days of putting on the epoxy primer . The high build primer is like liquid bondo which will help to fill in scatches from the lower grit papers and also help build up low spots and waves in your body panels when you start block sanding to prep for paint. Once you get to the high build stage and start your block sanding, you probably don't want to use anything less then 320 grit for 3 or 4 coats of high build. Final block sanding before paint should be no less then 500 grit. Once you get your first coat of paint and you like what you see, wet sand with 600 and spray your next coat of paint, wet sand with 1000 and spray it again. Then put 5 or 6 coats of clear over top and you will have a paint job that looks about 3 ft deep. Buy or go to your local library for books on body work and paint. If they don't teach you what you need to know about doing your own body work and paint they will help you to know what your body shop is talking about if you go that route. Start in areas that won't show as badly like hidden parts, interior or engine compartment. Hope I haven't overwhelmed you.
