Why the NI?
Have you ever been to NZ - travelled around, taken a look? When I came I was told that Christchurch would be a great "fit" but as soon as I got there I realised (pre-quake) that it was not for me.
Do you want to live in a big city (there are no big cities, but in NZ terms, Auckland, Wellington, Christchurch) or something smaller but which still has facilities (Dunedin, Nelson).
Transport in Auckland is terrible.
Do you have medical needs - Nelson hospital is in a bit of crisis at the moment...
Education - schools are often smaller and single sex education is very much a thing. Church schools are generally "better" but costly (even the integrated ones ask for substantial donations). Small towns may only have one High School.
What do you like to do in your spare time? Shopping - stay in the UK, outdoors - move to the West Coast of the SI.
Food is very expensive. Capsicums currently over $4 each because out of season. Cheese and butter are absurd (especially as dairy is our main industry!).
Housing is not cheaper than the UK but you may get a house in a far nicer area/outlook - a home close to the sea/beach is not that unusual. But take care - many are still poorly insulated and heated (many heat with wood and some even still use coal, welcome to the 1950's).
Racism is a real issue even if many NZ's can't see it. Casual jokes about Chinese drivers and Indian shop owners are common and folk get all "but it's true..." if you pull them up on it. Maori and Pasifika peoples tend to have worse educational and health outcomes due to historic inequality; we are working on this as a country but have a long way to go.
It's a REALLY long way from anywhere...no more popping over to Barcelona for a long weekend and forget thinking that you can do the same and just weekend on Rarotonga, it costs too much.
You really need to come and take a look around.
I love it.