First let me say sorry for all the problems that you have had in your life. I am sure this trip would help ease some of the pain you have experienced.
Now onto the traveling the U.S. I too live in Australia and am an American Citizen. I have done two tours of the states in the last six years, ridden over 45,000 km in the states and Canada and have been to all the states west of the Mississippi including Alaska.
Before you start booking your trip are you aware that the U.S. government will only give you a three month tourist visa? It would be good if you could apply for an extended one before you book all your flights etc. My wife (girlfriend at the time) was rejected for an extended visa on our first trip over.
Some of the highlights of our last trip had to be Moab area of Utah for off road riding. Arkansas for the scenery, great food and twisting roads, Wyoming for the national parks and Alaska for the beauty, isolation and some great adventure riding.
Good luck with your trip and PM me if I could be of any help with your plans.