1) The typical rate, as far as I know, seems to be around 10%. This means that the 100% delegate will receive 90% of pay while the IT person will receive 10% to run the delegate.
2) There are some tools that are more popular than others. Alt, Xeroc, Emski, and Wuoko have all written custom feed scripts and many delegates customize them further to provide better focus on what they may feel is an under served pair (for example, OIL). Also the polling times of all the delegates vary greatly by how they've configured their feed so even if a number are pulling from the same source the time variations will add the needed diversity.
3) There is no technical limit on how many delegates an individual can run but the community seems to frown upon any more then a few.