I often fly to/from NAN from SYD or AKL. QF codeshare with Air Pacific but you only get QF rather than oneworld points. The NZ offering to NAN is not as good as Air Pacific in terms of service. Connections from the BA flights at SYD are easy both ways because of the timing.

The SYD to NAN flights are in an ex QF 747, J class is in old fashioned but big comfy seats.

I have not flown the NAN - LAX sector on Air Pacific, but they use the 747 and the service is old fashioned so take a computer or IPAD for your own in flight entertainment!. They DO have seat power (OZ/US/EU sockets).

December in Fiji is the hottest time so avoid Suva which is both hot and WET... better the hot and dry climate on the other side of the island.

A final note.... the Air Pacific online booking "engine" is pretty bad at keeping up with traffic (in my experience) so if you book for yourself online, keep saving screenshots as PDF's.... this has saved me a lot of hassle in the past.