Trying to understand micro-hydroelectric power...

I understand the concept but I have difficulty understanding some of the things that can happen in real life... For instance,

1) Will "any" river be able to sufficiently power the home?  Its said that 300W is good enough for most home, does that mean 500W is good enough for bigger homes?  And if 500W is needed... how do you know the river can provide that kind of power?

2) What about the new stuff coming out... like tankless water heaters which seem to consume a lot of energy when it is "turned on"... will a micro-hydroelectric power provide that kind of power "instantly"?

3) I understand that most rivers will flood in a 100 year time frame... what happens to the turbine during such event?  Will it be knocked off and flow downstream?  Will it short and create a home hazard?

4) If my "land" only has 60 feet of river frontage, does that mean I can't use any more than that even if the river stretches for hundreds of feet on both streams...

5) Can a lake be used to power it or is it only for rivers? 

6) What if it is a highly used river?  Will kayakers be in danger?  Should I cordon off the area?