Hi Michael and welcome to the site, and Australia.
As to your questions, I'm not sure if you US license will be valid here but it can quickly be verified by contact yoour new stats transport dept. If QLD, that would be Queenslend Transprot. If you are after some work as a skipper on a game rig, might I suggest Cairns (where are you located?), if you are willing to travel up there, as the giant black marlin season is just beginning, and if all your licenses are valid, youw may find yourself picking up some work pretty quick as the game boats are high in demand over the next few months (till end of Feb).
Cheers,
Scott