how bad is the priming job? if it's really bad, use a coarser paper and work to a finer grit. start with a 150 grit dry and work down to a 400 grit wet. fill the holes w/ bondo, make sure to sand those down evenly. doesn't matter wat type of primer you use because the paint will go right over it, white is usually good tho.
u can get mesh grill at home depot. cut it about an inch longer than the actual hole. do not epoxy/bondo it onto the bumper because you don't want to have that painted along w/ the bumper. use bondo and apply about 1-2" lengths of wire onto the inside edges of the hole. it should look like a Q tip. put the grill over that and bend the wires outward so that it holds the grill in.
that's all i can say. if you have any other questions, just post them up. good luck.