Yip, plan on shooting from the sitting position. I went upto Casper, WY. for a 3 day prairie dog shoot this summer, and on the last day we were there, three of us went on a "walk about" to reach parts of the ranch that we weren't allowed to drive to, and it was the best shooting we had. Around Wheatland you'll find gentle rolling hills, some sage brush, and wide open spaces. You could even have some deep wide gullies that allow you to sit on the edge and look down into a valley with prairie dogs, that's my favorite shooting position, above looking/shooting down into a valley.
Yip, you'll need to keep an eye out for rattlers. Two guys in our group saw rattlers near Casper. No near misses though. Not a lot of snakes, but enough so to be aware of where you're walking. There were 14 of us, and only two guys saw snakes.