You get the licence from the FAA on the basis of your Aussie one.
You need a check flight (like our biennial flight review) to exercise the privileges of the licence (license over there
) If you get a glider license you can do the check in a glider, it also covers you for anything else on the license (I got SE land and ME land)
Aussie (ICAO) class 2 medical OK.
To get an Instrument rating added you need to do an online exam.
I am unlikely to bother doing that, prefer VFR for joy flights.