riding on Australian Bike Licences ?? and buying in the US ??

Gday ,
Me and my brother plan on riding across the states in june , But we dont know where to start on the list of things to do before getting there..
Firstly My brother has a full Licence in Aus (which means he can ride anything he wants ) But I only have my L plates which means I can only ride 250CC and below (may aswell push the thing!!) , I want to buy a Monster or a Enduro bike for the trek (From LA to New York with 5000miles of detours ha ha ) , Does anyone know if the rules/condistions to my licence are the same in the states , and / or what are the rules for L plate riders in California ??..

We are going to be riding with another mate who is also buying a bike there , Are we able to get insured on all bikes regardless of which country we come from?, I have an address I can use in LA and one in New York if that could help us..

Any help would be greatly appreicated ..
Thanks
Nic Grogan