Your revised schedule looks very doable and enjoyable. In 2005 we did something similar for 8 weeks all the way to the west coast. We moved basically every other day with a few longer stays at Grand Canyon, Kings Canyon, and Yellowstone. If I had the chance would do the trip again.
Looks like you will be in Monument Valley for Memorial Day, arriving on Saturday. This is the only time you may want to make reservations or arrive a day earlier on Friday. This should be the only weekend where you may have problems finding a campsite, but your location may help you out. Will let others chime in that know the area.
Even without a toad, agree with the others about a central location. Though, staying two nights in Arches then moving over to Dead Horse Point SP would be idea. Especially if you can go four nights without power. May be able to shave off a day here though, since the move between the two will only take an hour unless you go to town to restock.
Enjoy your trip, looks like a lot of fun.
