2 self tappers is my no1 but if you decide to use tape get a panel wipe/pre paint wipe and really clean where your going to stick (any old chemicals/grease/cleaning stuff = fall off in no time with sticky!)
you don't need to remove the bumpers (and most cars have holes where the original plates were) and just buy a screw to fit that (if not then m6 or 8 and about 15-20mm long)