Amatuer,
Do you mean FAA PPL based on a foreign licence? Your CPL will get you a FAA PPL but to exercise the privileges of the PPL you must have both medical and BFR current. As you dont need a CASA class 1 for a PPL you should be fine. If you are planning on joining a US regional you will have to get an FAA class 1 anyway. Dont bother getting your FAA PPL based on Oz licence. You can just do the FAA ATP checkride without it.