You time frame sounds doable, but daily mileage is certainly an individual preference. I find that anywhere between 50 and 80 miles per day including rest days and half days works for me.
I will say that I always find that it is much more satisfying to not have a firm deadline though. Much better to have more time and money that you think you will need. That allows you to just take things as they come. Whether you feel like riding consecutive 100+ mile days every day or taking a few days off to see a national park or whatever, it is nice if you schedule can accommodate your spur of the moment choices.
BTW another option that will allow flexibility with a fixed time deadline is to have a flexible end point.
Where possible I ride from the end of the tour that requires the most consideration in travel, ending in the location that require less advance notice for airline, bus, or train tickets. If I can finish the tour close enough to home to either ride home or be picked up, so much the better. If you have a friend or family member who is an airline employee willing to share a friends and family pass, flying standby on the trip home might be a good option that will allow finishing whenever you happen to get there and even from variable end points.