Very good answer above so only a couple of mild additions. Much your trip has been covered in prior threads so punch in 'Montana' and Missoula into the search function.
Only concern I have (all the places you want to visit) is the plan may be too ambitious unless you really like spending HOURS behind the wheel of your car. You might want to hit a web site like 'triptic' and get the mileage between locations. From personal history, even on Freeways, you will only average 50mph with stops. Or to put that (as I have in the past) 800 miles will eat up the better part of 16 hours.
Oh, in Montana its a long way between petrol stations! Plan ahead.