Take a wander around the CASA website
http://www.casa.gov.au/avreg/fcl_lic/index.htm] Recognition of foreign licences[/url]. It should answer a few of your questions. I believe that the PPL licences are comparatively easy to convert back to JAA ones. Check with your authorities.
Take some time to look at the CASA site. There's some good info there.
Enjoy.