First, it's a huge area. Enormous. There is a ton of public land. Deer densities aren't tremendously high. Expect to do a LOT of glassing. You could find yourself a long way from any amenities, including gas so plan well. Rain is a killer because of the gumbo. Take chains, but realize if it rains you might not be driving anywhere until it dries out.
Curious because you mention HD700 also. Are you planning on hunting both sides? The CMR has its own regs on mule deer hunting and closes earlier than the regular general season.
Be prepared for tremendous changes in weather. It can go from 70 and sunny to below zero and snowing in the blink of an eye.
Take lots of pictures.
The Missouri Breaks are phenomenal. Be prepared to do a lot of hiking and glassing, and glass hard. There is so much cover it'll make your head spin.