Montana... cold country... deep litter bedding. Consider how you plan to deal with frozen waterers. You'll want electricity in their coop for lights, and at least one electrical outlet for an optional heater, incubator, or brooder. Chicken math... 12 to 24 hens, plus a rooster or two, get lucky with a broody hen, or four... 60 birds before ya know it... plan for it, it happens to all of us! Lots of predators in your neck of the woods, so do your best to predator proof their home and consider aerial attacks too. Costs less to build a good fence the first time, than one 'that will do' until it doesn't.
Couldn't agree more with sourland, come cold season, your flock will be spending a lot of time in their coop. A large coop will allow your birds to avoid any of them that are suffering 'cabin fever' (overall grumpiness and picking fights).
The minimum rule of thumb is about 2 to 3 square feet per chicken inside the chicken coop, more for you as it's unlikely they'll want to use a run in the winter for a long time, and 8 to 10 square feet per chicken in an outside run. More square footage is better. Skimping on space requirements for a flock of chickens can cause stress, cannibalism, pecking, and sometimes even death. With 5 acres, you may decide to free range them in good weather, but expect some losses if you do. Enjoy your flock!