I am planning to shoot Grand Tetons and in the Yellowstone, as well as in the Black Hills of South Dakota in September, probably from Sept 4 through the 15th or 16th.
I am thinking that time of year it will be safe not to make hotel reservations so I can be free to go and come as I please. Also, wondering about the weather that time of year.
Any input would be greatly appreciated.
I am less familiar with Western Wyoming than I am with the Black Hills. It has been about five years since I visited the Tetons while I visit the Black Hills about twice a year. September is a good choice. However, not all years are equal. There are some years when the changing Aspen trees are simply breathtaking and other years merely beautiful. The Black Hills area is quite large, by the way, and the scenery is different throughout -- the southern hills are much different, for instance, than the northern area and different still from the Wyoming bits.
In any event, I wouldn't worry about hotel space; in my experience there is an overabundance of hotel space there... particularly at that time of year. Rapid City would certainly have vacancies. As well as Deadwood... or Newcastle... or Hulett, as far as that goes.
The Badlands south of Rapid City are also photographically interesting in the morning/evening hours. (As if you are looking for more ground to cover. I actually doubt you will get to everything you have planned in that time span.)