1) Ultrapeers will increase the horizon, at least in BearShare anyway.
2) BearShare 2.5.0 has swarming now. And believe me it is sweet! Downloaded a 200mb file from 14 different people at the same time, I got that file in under 10 minutes.
3) That would be nice.
4) Definately a no way for this one.
5) It has been called "Tiered uploading" in other places, and would be a great feature.
6) Sorry blocking is just not the answer.
7) The way you do it doesn't really matter. That only thing that is important is that no half downloaded files get accidentally shared by the client.