Here's a sampling of threads that will probably answer a lot of your questions:
Seeking Westwater advice
when is WestWater most rowdy?
Westwater this weekend - 25k+
Westwater at high flows
Have fun - IMO the characteristics you've seen above 17K are about the same as what you'd see above 10K. Not much difference in the rapids, other than the eddy lines get more burly the higher the flow (not surprisingly). Flows from 4K to 10K will be within the abilities of most competent rowers; the only caveat being that I consider Skull to be a no-scout above about 12k due to the difficulty of getting out of that eddy. As long as they're cool with that & the possibility of a long swim + have some big water experience, then they're good to go. Save a spot for a safety kayaker.