I don't know whether to add condolences or congratulations... In either case welcome to an interesting city about as far as you can get from New York.

You don't say where in the USA will be your destination. The reason I ask is that Cathay is one stop to more destinations in the USA than the local brand. And while admitting that CX PEY is not quite as good as QF Y+, both credit 1.5 EQP to the AA program. OTOH the CX program does quite well with the unpublished benefits. And after getting CX SL (at 30K points) your 2 round trips PER->USA will yield at least 48K points toward the 60K required for CX Gold. Though your return to the USA moves the choice towards AA. Consider where you will be flying after the two years. The lack of a soft landing now by AA has certainly influenced my thoughts. And the changes to the AA million miler program make it a fantasy for most people just starting serious flying.
You might consider a QF account, if domestic travel on QF will be a serious part of the stay. E class, the normal domestic economy sales category credits only to QF. O and Q credit token amounts to AA and none to CX. The QF account is free if opened before arrival in Australia or in conjunction with the local grocery discount program at Woolworths(Aus).

The second thing to consider is that almost all tickets are one year tickets now and while the fall of the Aussie dollar has mitigated the insane local prices, I think you will find that exUSA pricing on PEY (or Y+) will still be lower than exPER.

I find that a night (or two) stopover in Hong Kong (same time zone as Perth) makes the entire trip more bearable.

On the credit card, consider in what currency you will be paid. If US$, then by all means get the credit card(s) before you move. But when you get here get one (or a debit card) locally for day to day usage.

YMMV but happy wandering

Fred

PS: If you add an AA connecting flight in the USA to the international long haul, that would complete the 4 AA segment requirement with no extra. OTOH almost all AA flight classes credit to CX or QF.