I have some information to post regarding international transfers at Sydney airport. The good news is that you can do the international transfer without having to go all the out through immigration and customs. The bad news is that it still takes 60 minutes minimum without checked luggage, on a good day, to make the transfer.
1) Air New Zealand does NOT offer online check-in so you cannot get a boarding pass before you fly UNLESS another partner airline is able to print one for you. (I could not get one from my carrier in Japan)
2) Even though I did NOT have a boarding pass for my Air New Zealand flight, I had a printed copy of my itinerary and was able to pass through the International Transfer Security checkpoint WITHOUT having to go through immigration or customs upon arrival from Japan. (This is contrary to what Air New Zealand staff told me pre-flight, but consistent with what the flight attendants announced during the return flight to Sydney.)
3) After passing through the International Transfer Security checkpoint, there was a VERY long line at the Sydney transit desk. Air New Zealand had only two staff members and it was about a one hour wait to get my boarding pass for the next flight. Other passengers who arrived later were able to go directly to the gate and get a boarding pass.
4) Air New Zealand would only issue the boarding pass for the first leg of my journey. Once I cleared immigration in New Zealand (and I WAS asked to show them my printed return itinerary documentation) I then had to go to the transfer desk in Christchurch to get the boarding pass for the second leg of my journey.
I had no checked luggage. The reality is that you can go through the Sydney International Transfer Security checkpoint, then go to the gate if time is short, but I would still allocate at least 90 minutes in the future for an international transfer in Sydney. This was in the morning, and I was lucky that there were not very many people going through the international transfer area. Since you have to pass through security, all rules for liquids and carryon apply, regardless of what airline you travel.
Checking luggage would have changed everything because I had two separate itineraries. I would have had to go through immigration in Sydney, collect my luggage and then clear customs before going out to the check-in area and dropping off my luggage on the second carrier. If you are going to do an international connection, it may simplify things to have the tickets re-issued so that all flights are on the same record locator. As long as the luggage is checked through to the final destination, there would be no need to clear immigration in Sydney for an international transfer.