That's a good way to deal with a mid-life crisis. I pedaled around the perimeter of Oz and covered the area you are talking about nine years ago.

Good luck finding a group of people all crazy enough to ride the Nullarbor. Actually it's a good ride if you like desert scenery which I do. Don't be swayed by doing it alone. You will no doubt run into other cyclists.

I don't think you can do better than the UK for a quality touring bike. Anything in Australia will cost you quite a bit more and you won't find the variety. I would buy one where you live and bring it with you for sure.