Having many years of touring experience I can say that preparation is over rated. Get in decent shape to ride 30-50 miles a day, pack light and ride. I am doing the Southern Tier in the spring and plan on doing a lot of the planning on the fly. That means planing a days ride the night before if possible. Even then, things change. There have been days when I planned 50 miles and only do around 30. There have been days that when I get to a destination I find I'm early, feel good and just keep on riding.

In short, have a tentative plan but don't feel committed to it. Take time to smell the roses, meet people and see things. Don't be in a hurry to get to the end of your tour, which by the way, happens quite often. Enjoy your adventure.