I’ll take this one.
No one knows, and I’ll add that at this point, power levels are pretty meaningless. If you want to figure out who is going to win a fight, ask yourself what story the writers want to tell. It sucks but it’s the way it is.
Unclear, and it’s being debated as to whether she has one at all.
Depends on your perspective. She did empower Tyrande as the Night Warrior, and that debatably allowed her to, with the assistance of Shandris and the champion, rescue what appears to be the majority of the Kaldorei souls in the maw, but your question is pretty expansive and gets into a LOT of topics. We know that Tyrande is being benched for the Sylvanas fight more specifically, but there are also long term questions about what the Kaldorei are going to be going forward and whether their culture and way of life will survive.
I don’t think that her being the Winter Queen’s sister gives us any information about their relative powers, especially again given that power levels don’t matter.
That’s a theory, she could be.
For your own sanity, don’t. You’ll be hoping for a very long time. Blizzard has finely tuned the delicate art of upsetting people and letting them down into a science.