Only you can determine that. What is your tolerance for sitting behind the wheel? Where do you want to stop and what do you want to see? On a trip like you are planning you have to be flexible with you itinerary so that might mean you find you want to stay in a certain area for more days than you initially planned on.... or less days, either way.
On our big circle trip we covered 8635 miles and took 10 weeks. Northern route out to the Olympic Penn. and southern route back home. Sometimes I drove 10 hrs a day other days it may have been 5 or 6 depending on the next destination stop. Don't over think things but have a good idea of what you want to see and do and go with the flow. We only made reservations for our destinations where we stayed more than 2 to 4 days. Any overnight stops were on the fly and we never had a place say they were full up. We used the RVParky app to find those overnight stops.
Go on-line and order the travel planners for each state you plan on going to. They are a wealth of information and give a good insight to what you may be interested in seeing....even things you didn't know about. Its a big beautiful country so take the time to see it up close. Can't beat the RVing experience doing that.