There is a boat slip at the first bridge below town, let the nearby house owner know what you're up to.
There is a couple of camps in the canyon above Cow Creek, several more in the vicinity of Cow Creek (pit toliet). Nothing below Cow Creek until the Snake. Mixed private and public lands along the river. Also poison ivy is thick.
I wouldn't go lower than 800 or 1000. Depending on what you think is fun..
Continuous class 2/3 above Cow Creek, pull drop class 3/4 below, quite a few in the last 4 miles.
Then 24 miles of Snake lake. The only good thing, when the Imnaha is running the Snake and the Salmon are pumping, regardless plan for a night on the Snake.
Logistics for shuttle aren't great, call ahead if you plan to hire.
It's a great canyon and fun water, good luck