My one piece of input is that the first half or so of the trip is very shallow (until the Henrys Fork confluence). So if you do it in a raft expect very slow progress and to drag onto the bottom of the river...a lot. Some people like the social aspect of taking it slow on the raft, but if you're less patient (like me), then a canoe or kayak will be twice as fast.

Also, if you hit the river in the evening or early morning you increase the chances of see moose, muskrat, osprey, cranes, etc.