Just make sure to take your time. Visit both the north and the south Island. Not just the South Island.
North Island:
Bay of Islands,
KeriKeri (So nice, they named it twice) with the first structure of Brick in NZ
Indeed the glow worm caves and cave tubing (black water rafting) in Waitoma
The Kuka falls
The thermal springs and geysers of Waiatapu with its Lord of The Rings scenery
The champagn pool in Waiatapu
South Island
Kaikura (have lobster there and swim with dolphins)
Ngakuta Bay
The glaciers on the South Island
Oh by the way, if you plan on renting a camping or using an RV, you might want to consider the camp sites that are maintained by Department of Conservation. they have a nice website as well (link here)
It’s so beautiful. Can I join you on your trip?