-THe most useful feature would be the previewing/running the file while downloading(at least the first segment)
-the possibility of multiple selection of files from the transfer window for multi-pausing/resuming
-malually defining the number of downloads

and one thought about the upload limit:
i'm afraid that by combining the upload with the download limitations(by explaining that a low max upload speed will limit the download speed) you are doing the opposite of what you intented : you are "pushing" the user to become a freeloader!
If i can't have a descent downoad because my bandwith is struggling by a speedy upload, the next logical step for me is not to share much (or not at all) in order to avoid it.