Hello and welcome to the RTA forums !

You will get differing opinions from people as it's 'different strokes for different folks' and thats the beauty of the road trip, getting to do what works for you ! The first thing to remember is that the US is huge and distances are great, although generally easier to cover than in the UK. An example of this is when you say " visiting Yellowstone while in the region" when it is 750 miles from Seattle and nearly 650 to Banff. It's fine as long as you know what you are getting yourself into, and Yellowstone is a place that really needs 3 or 4 days just to get around and see the highlights, so you haven't got a heck of a lot of time there for the investment in mileage. You certainly have time to do what you have planned and it will be an amazing trip, it's about 4 days dedicated to driving which isn't bad at all over 2 weeks. Your stops look reasonable to me, you could even push a little further than Missoula, perhaps Deer lodge to put you closer to Yellowstone. Although that would put you 'in the saddle' for around 10 hours with stops.

Book Yellowstone lodgings asap, you may already have a few problems getting a good choice.