1. No. Only units can be supported, not power or garrison tokens 2. Uncertain, never really used tides of battle. 3. No, support and defence may be played as many times as desired per turn 4. I'm not sure I understand your question, but I believe the answer is no. You can only support adjacent areas, you cannot support across seas. Similarly, a land unit cannot support a sea unit. Hope that helps!
Thansk for the clarifying answers
I´ll try to clarify question 4 by breaking it into several questions:
For example, Player A has one boat in each of the right side sea areas(quite extrem, I know). He has a march order in Storms End and a Support order in Sunspear.
4 a: Player A can attack Winterfell from Storms End, correct?
b: Can Sunspear units support the attack?