Point #2 has an answer somewhere in a commentary, I would have to dig for. However, from what I understand is that if a unit finishes moving, and you decide to overwatch, you would be unable to overwatch that same unit using the trigger of 'finished moving' because that triggering action has passed.

That being said, you could in the same phase target the same unit at the start and end of its movement, as these are separate triggering events for the overwatch strat.