The PE 77W seats are far better than 77E seats but be aware not all flights ex LAX are 77W, there are still a number of 77E flights on this route.
You won't be able to select PE seats to SYD with *G, automatic seating in PE (if available) if only a Air NZ status benefit, but there is probably no harm asking at check-in to see if there are spare seats.
As for LAX lounges I've only visited the Air NZ one in T2, Air NZ do move to TBIT in early December so you'll pass through a different terminal on your way back. Koru in SYD is also closed at present for a major refit which is discussed in another thread in here, visiting the SQ lounge there may also be an option as it's quite nice.