With QF you cannot select seats until after you pay. To me a major disincentive with QF, unlike many other airlines where you can select seats before payment.

PE is a separate class and you do not get for free. Is not "preferred seating"
Exit rows also require payment, but if your family (kids?) are young you may not be eligible.

You cannot upgrade QF flights with AA ff miles.

SYD is not the only international airport in Australia. BNE & MEL also have flights ex USA. If SYD is not the main destination, also consider Air NZ IAH-AKL-Aussie. AKL to XXX in Australia is just as easy as SYD to XXX. DL & VA also fly LAX Australia.
Route maps--->Great Circle Mapper