Somehow I missed your original post. My wife and I, along with some friends, did this exact cruise 5 years ago. In fact, we crossed the International Date Line on April 15, 2014. As you know, the cruise itself is 18 nights, of which you have something like 12 sea days. We did some pre-nights in Waikiki and Sydney. On the back end, we spent 3 nights at Aulani so we were gone a bit over 3 weeks. We were in a Grand Suite and had friends in an Owner Suite and a regular outside cabin. Plus we met a very nice Austrailian family on board who were in a veranda cabin.
Our pre-nights in Sydney were at the Marriott Circular Cay. Its very nice and convenient to lots of stuff. One day we went to the Sydney Zoo, which you get to by taking a ferry from Circular Cay. Enjoyed the zoo very much. On the way back we rode the ferry around Sydney harbor and made a stop at Manly Beach, which I had visited in 1971. On the day our ship departed we simply walked (rolled) our luggage down to the ship which was just a block away.
The two stops in New Zealand were just OK. All three stops in French Polynesia are really spectacular. And we really enjoyed the stop at Maul before the cruise ended in Honolulu. Life onboard the ship during the sea days takes on a relaxing rhythm. There are always activities to do if you want. There was a polliwog ceremony on the day we crossed the equator going north. I remember at one point the captain announcing that we were something like 3,000 miles from the nearest land!
Hope you enjoy your sailing.