Hi Kunney, how much sanding and to what grit will depend on the finish you use. Probably 320 is fine enough for staining, once you get the clear coats on you can go down to the finer grades to get that glassy smooth finish.
If you want a fender shape, a google search will find plenty of PDF's you can download and print, cut out and trace. The main thing is not to take any more than what fender did , within reason.