89
If the users are forced to rate and comment a song before being able to download another, you'll end up having problems from users. The ratings won't be very accurate and comments might consist of just a few words, complaints, or just "fhkdjsahf" so they can get to the next download. People will rate things low just because they are annoyed with having to rate it.
what is redaktion?
With the ability to specify how much space a group has, or how many files they can upload, you should have the ability to make one group 0. Still, downloads from any external source won't count in their stats though...only if they download it through the link on your site.
Commenting a second time, I don't see a problem with, but rating a second time would be a problem. That would definetly have to be stopped. Otherwise you'll have people voting for their own stuff tons of times over just to be number 1. Good call with that one. I hadn't even thought of it.