1. You can do this with the additional tagging tools plug-in setting that tag to 0
2. You seem to misunderstand what "Random" means. "Random" doesn't mean "everything plays evenly." "Random" has no memory of what has come before, therefore the fact that something has played before is irrelevant to what will be played in the future. If you want to play your entire list shuffled, your best bet is to shuffle the playlist and then play it in the order that is generated. Shuffle the playlist, set that as the natural order, and then play songs 1-15, come back the next day and play songs 16-40, etc. You will not get repeat plays in this way.