I've whitewatered the Snake, but not sure what stretches. I was the cargo hauler for a friends whitewater company. I can't help you much on most of this. I followed my friend's lead. But, I would try looking for on a websearch for "NWRA" or "NorthWest Rafters Association". An old whitewater club that tours around the NW hitting whitewater rivers. May be able to hook you up with when/where to go. I knew alot of guys in the NWRA, I ran with most. Never became a member, since most were involved and I tagged along with my boat. I'd go to the trout section or the worldwide fishing section and ask about lodging and things.
Wish I could help you out more. Haven't run the snake in a decade, so a bit rusty. We did a tour, and did the snake, then the Colorado and a few other rivers. I do believe the Mountaneers still have a publication on whitewater rivers. I do believe my whitewater guide for WA was produced by them. Very indepth and accurate run info on rivers and ratings per water levels.
Sorry, about best I can do for you.
"Good angling ethic is not a monopoly practiced just by fly fisherman" - Bill McMillan