Gerry,
At the moment the guys doing their command have been here 10 years. Suspect it will be more like 15 years for new joiners.
Regarding the basing in Oz, I don't think your chances are very good for many years to come unless you don't mind being stuck on the freighter forever.
If you joined today you would have approximately 500 Aussies in front of you and with only limited slots available it would take a while.