Sounds like cycling isn't something new to you, so I think you will find your rhythm quickly. That was true for me on my first tour: Seattle to Bar Harbor, ME then home to Philadelphia and on to Ocean City, NJ. While I had been cycling for many years and had done a few week-long supported tours, my loaded riding experience consisted of not much more than a moderately hilly 62 mile ride one Sunday morning a few weeks before I headed to Seattle to start the trip. And I had never camped before in my life.
Starting out with relatively easy mileages is a good idea. Our first few days from Seattle up to the intersection with the NT near Anacortes were pretty easy. The next two days, before we crossed the Cascades, were also fairly easy mileage and terrain-wise, although one of them was spent riding in a cold, steady rain. All that was good preparation for crossing the Cascades, which we did the snow.
The camping part of the equation took some getting used to. The first night I slept very little. Sounds (including those coming from the very loud snorers in our group of 12) kept waking me up. After a week or so I got used to it.
I also agree that rest days are best left for places where there are fun/interesting things to do. Our rest days in Glacier National Park and at Lake Itasca were nice as there were non-biking activities to pursue. In contrast, our rest day in Glasgow, MT was downright dull. Not much to do in a place like that. I remember being so bored on our day off in Minot, ND that I went to the zoo and then to see a movie at the mall. I could have done that at home. But I was with a group so compromises had to be made.
Can’t offer any insight into the commitment aspect as my situation was somewhat unique. For almost two years I knew I was going to lose my job due to a merger. As that time approached, I begged to be let go in early May so I could take the trip. I got a decent severance package and had no house, spouse or kids to consider. Since I wanted to take the trip, committing was easy.