The heat isn't a problem. It gets pretty hot in Canada too, and yes, I was in Australia during their summer.
I'm starting my ride in Davis, California because I am planning to ride the Gold Rush Randonnee:
http://davisbikeclub.org/goldrush/default.htm
Then I'm debating if I want to tour around the south, and then fly back, or if I want to cycle back toward Canada.
A lot of it depends on job situations and how much time off I have too.