1. If there are units belonging to other Allied powers in the territory, control is established using the rules for moving all units on one side out of a contested territory (see “Land Unitsâ€, page 15 of the rulebook); otherwise the territory will be uncontrolled until another power moves into it and will not mobilize units when entered.
2. As above, and they are treated as minor neutral powers for the remainder of the game.
3. No.
4. Subs may submerge instead of firing in any round of combat. However, they are still subject to enemy fire while attempting to submerge. In your example, the sub may attempt to escape by submerging instead of firing in round one, but the cruiser will still get one shot at it.
5. Only as cargo on transports.