If you have tires that can take dirt/gravel, take the Old Darby Alternative between Hamilton and Darby. It's really nice back there.
It's a long 75 miles. From Darby on you climb gently to Sula. A few miles after Sula (good sandwiches at the store there), things get steeper. But what really makes it a long 75 miles is the stretch after Lost Trail Pass. There is only a few miles of steep descending before the grade eases and you have to do a lot pedaling to get to town. But it sounds slike you will be travelling on the light side.
The people at the Nez Perce were really nice. When we arrived early eveing, they were away at a family function. They left envelopes with keys to each room taped to the office door. There was also a note explaining that we should simply pick a room and that they would be back later that night to collect payment.
This is pretty much the only place to eat in town, and it's pretty good:http://www.thecrossingbarandgrill.com/
They have a neat bar decorated with cattle brands. Note that the grocery store in town closes pretty early. 6 p.m. IIRC.
Don't miss the truck in Sparwood. There is a cool cafe/ cofe shop in an old church on your right in Coleman. Pincher Creek is a sad little town. IIRC, other than the Prince of Wales Hotel, the number of rooms in Waterton Village are limited so you might want to make a reservation. Same thing if you want a room in Glacier, N.P.
The Park Cafe in St. Mary is the place to eat, especially if you like pie. Before you get to St. Mary you will pass a small eatery on the left side of U.S. 89 called the Fire Horse Cafe. It's on the Blackfoot reservation. Had an excellent, hand-pressed burger there.