A nomadic life style like you are thinking of can be very rewarding and a lot of fun. Now, the "but", for instance, say you're in Moab, There are a lot of camp grounds and sites but, breaking camp everyday may not be convenient only to return at days end and set up camp again. The remote sites at Arches NP, are not always easy to get to and parking is often hard to find while you're driving an RV.
If you want to photograph down in the Canyon, for instance, looking up at Dead Horse Point or the confluence of the Green and Colorado Rivers. Not to likely in an RV that you can call home.
In plain English, camping and exploring are not always compatible when using the same vehicle.
Expand your thoughts to include say a Jeep or Suzuki with a Class B or C. We see folks towing both with smaller RVs. It cuts into stealth camping in some ways but it allows you to go further afield for those shots no one else has.
Our neighbor is a professional photographer, we were invited to dinner at his and his partners home the other night. It was the first time in the house and they have decorated with his and David's photographs. There is one that is one of the most beautiful shots of the Grand Canyon NP, that we have ever seen. He sat and waited for three hours for that shot. Up well before dawn and drive to the site, not always easy even in a VW Westie.
The rest of your questions are sort of easy to answer and you've gotten some good ones, the choice of RV not so much. Take your time, maybe rent as suggested, maybe look around at B's, C's and even small A's and towed vehicles, look at small bumper tow trailers. Lots of really neat stuff available both classic and modern. Spend some time camping in organized campgrounds and parks and wandering around talking to others whose wheels don't get flat on one side. Try Moab in a rented C, find out if it is capable of getting you out into the areas you are interested in photographing.
Just a little bit to think about. Good luck in your search and most of all, Have Fun.