+1 for this, since i'm sharing bandwidth with my ol' folks and i can only download/upload from 2 to 9 am.
Yes, either a Scheduler or a "Favorites" section that will hold downloads in a "wait" status until told to execute.
The scheduler in uTorrent would be a great model to follow. It gives you a grid with 7 rows (days of week) and 24 columns (hours of the day). In each box you can click to toggle it through 3 choices which would be represented by colors or symbols: idle (no traffic), a "low" maximum KB/s setting (which would need correspondingly low # of slots in Soulseek, probably), and a "normal" maximum KB/s setting. Very intuitive when you see it in action.