...I'd suggest you postpone your cross country ride for a few years. Buy a road bike now. Ride it for a half dozen years. Ride 5,000-10,000 miles a year for the next half dozen years. Learn about bicycling. Then ride across the country....Thanks for writing this as you saved me a fair bit of typing. My first reaction on reading the OP was incredulity. These guys don't own bikes, don't know what type to buy, don't currently ride and don't say what, if any, charity they are trying to assist. Amazing.
Well it's a good thing that these two did not ask for your advice. Dave and Loretta, with no cycling experience, bought bikes and gear and have been traveling for several years now.
Dave -> http://www.tiredofit.ca/
Loretta -> http://www.skalatitude.com/p/about.html
I would have given them the same advice. Get a bike and ride for a half dozen years. The US and the rest of the world will still be there 6 years from now. When you know what you are doing, then ride across the world. It will be easier and more fun because you won't have as many problems. You will know what you are doing. Your advice reminds me of something. People win the lottery about everyday. You apparently would recommend the lottery as a retirement method and a way to accumulate wealth for a living. Of course people who know how the world works, would not recommend the lottery as a financial strategy. Lottery and waking up tomorrow and riding across the US with no experience. Pretty similar to me.