My advice - open a bank account. I did Westpac migrant banking too, VERY easy and found them very helpful - unlike Kiwibank, which my wife (a NZer) had for 10 years - yet they didn't want to know, credit cards, visa cards etc. were impossible, as is their customer services.
Mobile phone - if you're anywhere near a city, Two Degrees all the way. Cheapest calls, texts and data (although they have forced the prices of Voda and Telecom down), and if you have a device, get a sim only. They are also by far the cheapest if you call overseas numbers or texts from your mobile.
Landline - I got a Sky package with Voda, easy to install, use, more than enough data on unlimited plan.
Car - do your research before you come, trade me a good guide for prices. Remember, a dealer won't typically have service history for cars and virtually all are imports. Advise a dealer though as you get a warranty (unless you know a lot about cars). Although most are truly revolting vehicles, going Japanese is the best bet as cheaper to run and service usually. Some acceptable cars, Subaru Legacy Estates a good allrounder.
Tax - Remember to register with IRD for a tax number. You can do it at branches of the AA, but no longer from abroad before you arrive. Many employers won't take you without one.