1. I can't answer this one, I'm a rotorhead.
2. F4 and Lctrl+F4 can be used.
3. Depending on the initial setup, distance, advantage, AI skill level, and your Game-settings (Game Mode or Real Mode) - yes, sometimes it can be easy to shoot them down. Try from a disadvantage situation using "Real Mode", and it may be more difficult.
4. Most often used 'trick' for FPS, is to tune down the Water settings: http://forums.eagle.ru/showpost.php?p=928235&postcount=9
Tune down other settings as well while you're at it. Shadows off or Planar.
EDIT: o7 and Welcome to the community :)