Man, with the questions you are asking you need to stop and get some help from someone else. I don't mean to offend you, but dude, thats not the right way to go about that at all. First off, I wouldn't use filler to fix a dent. Second, if I did need to use a filler, it'd be fiberglass filler and not bondo. If you're going to paint a practice piece, do an easier color like white or gray. Try and get a part time job helping around a body shop if you're serious about it.