I cannot answer 1. 2. I find difficult to believe. If the inbound was at about 300 feet there would not be time for the departing aircraft to start to roll, let alone get far enough down the runway to be safe. 3. Whoever gets in on the R/T first.
Tight separations are essential at very busy airfields and the controllers and pilots are usually very switched-on. In good weather separations maybe reduced significantly when pilots and controllers can see what's happening.