The water is quite warm in September and early October. As long as the air temp is reasonable you won't need or want a wetsuit. Of course, if you have room bring one along though.
I did it last October. It stormed and the air temp dropped while I was on the river and I had my hands and feet in the water to keep them warm.
As far as camping in the second half, most of the good spots are designated BLM campgrounds. There are some other places as well. Note that river right is Arches Ntl. Park for most of the last part and I believe permits are required (I could be wrong)
Another note, there is a special fire restriction in force right now. No open fires 1/4 mile from the river and that includes developed campgrounds with fire rings. It most likely will not be in effect by October.