Yosemite1, I suggest you look carefully at that tour. Of the 20 days they claim, you only have 12 with "feet on the ground"---meaning actual activities. Four days are given to flying to and from the South Pacific, and another four lost to travel days. Day 9 they label "the Southern Alps" but you don't actually get there. In driving from Queenstown to Christchurch in a day, you go "toward" Aoraki/Mt. Cook national par, but apparently you don't actually go there. You stop at Lake Tekapo, "nestled among snowy peaks"---hardly. The lake is beautiful, but is in a dry plain surrounded by some lesser mountains/hills. They stop there for you to see a statue of a dog and the Church of the Good Shepherd. Nice but hardly a South Island highlight.
So 12 days to see North Island, South Island, and Australia? We spent 17 days on the South Island and covered some highlights, but there is so much more.
The Odysseys trip I suggested on your thread is the same price (around $8200 double occupancy) for a 23-day trip that includes most of the same destinations but more time at the main ones. They include all air travel in the price, and count 3 days (not 4) toward the travel to and from the South Pacific. They actually go into Mt. Cook national park and spend a night and some time there. They swap Alice Springs and Uluru in Australia for Melbourne on your chosen tour, but I think that is a good thing---we enjoyed Melbourne (a lovely city) but Alice Springs is an iconic Australian outback town, and Uluru a natural wonder. Their travel days are shorter increments, so you still have half a day one place or the other---not losing a whole day to travel. From Oz to Christchurch they travel in the evening, so you have most of the day in Sydney first. So time with "feet on the ground" is much more than the other trip.
Also there is a big difference in the number of dinners included in the trips---3 for the Holidays versus 9 for the Odysseys (not including flight meals) if that matters.
All of these trips are expensive if you choose a guided trip. We did self-guided (with more time in New Zealand) for much less than half the price, but that means some driving on the left, which some prefer not to do.
For Tess---seeing New Years Eve in Sydney is a worthy goal, but the tours that line up with that cost extra, and the hotels in Sydney during that time are expensive. Still worth it if you can make that work---it will take some advance planning. We arrived in Sydney on New Years Day, after a flight on which we missed New Years Eve---which is why we were able to score tickets in First Class with our miles. It was fun to see all the remnants of the party the night before. But we are not big "New Years people"---which is why I am on the computer right now. Going to a quiet party that does not start for an hour.
If you will be more specific as to what you want in a tour, or would consider independent---please let us know. And as for an apartment, where do you see yourself? City like Sydney? Or beach town?