All the suggested routes are great ways to head west to the Oregon/Washington area. The destinations mentioned are certainly worthy of your consideration. We have come close to many of the recommended sights, but the Idaho border at the Snake River was the limit for us after visiting some towns that were so captivating we unexpectedly reached our time limit and headed home again.
You can certainly head west using Lookout Pass and find yourself in Doubt quickly. I prefer to drive through, but many here will caution you to assess everything once you get there. Its a beautiful drive most of the year, yet there are snowy days which can cause a premature stop in Continent. It may be an age thing, but I found it too damp for comfort.
Coeur d'Alene was beautiful, especially the lake. Just south of there you can stop in Cognito. No one will recognise you there so you won't be bothered - very relaxing. The sights are almost as good a bit further west in Sane. They have no public transportation so you must be driven there, usually by family or friends but more likely it will be by other campers who ask incessantly how much your Airstream cost.
Since we turned back before entering Oregon, I haven't been in Kahoots. Apparently, the local custom states you can't go alone. You have to be in Kahoots with someone so take your bride along to do it properly. I'm told its as good as being in Flexible if you have a firm travel timetable for your trip.
On your way back, be sure to spend some time in Capable. I go there more often now that I am retired and have assumed sole responsiblility for our route planning. One of my other favorite places to be is in Suspense. It really gets the adrenalin up and rounds out the trip with a bit of a high as you head back into the Rockies on the road home that time of year.
No matter what you do, enjoy every minute of the trip!