Got new covers and are unpainted. My question is what parts to paint?

I saw someone left the bolt cut outs un painted? Seems that would be expectable to rust also.

Next, how far around the edge do you go? Should I go a little around to the interior to be sure nothing is left exposed?

 

you can just hit them with a good old rattle can...i never paint them inside though,paint chips floating through your diff is really not a good thing and out of all the old diff covers i have removed rust has never really been that much of a problem..the diff oil pretty much takes care of that