You won't be able to set the final pinion angle until the body is on the truck with the bed wood in, fuel in the tank, etc. You can just roughly set it at much less without the weight on it, but your best bet is to do the final setting when everything is together.
Check out
this article. The comments from Currie are what I agree with most, 1-3 degrees, and more than that is unnecessary and could result in other issues. If you're planning on carrying weight most of the time then that will help you decide on what your angle should be, but I would stay close to that 1-3 degrees. Keep in mind your differential and transmission centerlines should be parallel ideally, for the least vibration.
