Remember to focus on enjoying the ride, not just surviving and completing the ride. So that should factor into your route planning. Pretty and/or interesting, but a little bit longer is better than miserable but shorter. That goes, too, for planning how far to ride each day. Allowing yourself time to stop and read historical markers, or eat at roadside fruit stands, and to enjoy the communities and diners in the evenings can be the best part of a cross-continent ride.
One of my most fun/interesting tours was a 10-day "tailwind ride." A friend and his daughter on their tandem, and my daughter and me on our tandem. Started in Garden City, Kansas. Basically the very center of the Great Plains. Each morning, we checked the weather channel and then rode whichever direction the wind was blowing. No plan other than that, just an interest to see where we'd end up after 10 days of tailwinds. Only repeated one section of the ride, and ultimately ended up in southern Nebraska, east and north of where we started.
Good luck, and hopefully tailwinds coast to coast....