1 and 2 are already implemented. Check out the latest 3.9.8 beta for a robust filtering system. Swarming from multiple hosts has been a feature of LimeWire for quite some time. When it says, "Downloading from X hosts" that means it is downloading different portions of the file from each host and glueing them back together in order.

3 would destroy the network. Utterly destroy it. _Any_ automated search that runs at a specified interval will cause so much traffic that it will clog all pipes and cause normal searches to not be effective, resulting in even more of a need for repeat searching. There are different ways of fixing this problem.