1. Until the play is complete, Words of Encouragement's interrupt is still in effect, so you can play any enhancement (including interrupts/negates). That said, you only get special initiative once per enhancement - if WoE plays something that doesn't win the battle or stop the discard, then after that completes the discard kicks in again and you already used special initiative, so you can't interrupt.
2. Yes, the rescuing player can add sites to battle at any time, as long as there are no pending abilities.
3. I'm not certain on this one. If I had to guess, the battle would continue, to avoid infinite loop arguments.
4. I believe you are correct about Throne of Grace but I'm.not certain - it might work like special initiative.
5. Yes. This has been a combo for a while.
6. Yes, they must reveal to prove they have no valid targets.
Beaten to it by Aggie.