A couple of things about NZ-don't forget the seasons are opposite-Summer is mid winter here. You have to be prepared for bad weather-all year round. It is not California where once summer comes, the weather is stable. A bad storm can run up on you in an hour or so in the mountains. Situational awareness is very important. People have died from hypothermia there even with the hut system because they lacked proper gear.

Also, I don't recommend trail runners, but I am sure plenty of people use them. Even on the tracks, the terrain can be rough. I had a brand new New Balance lightweight boot come apart on me from being soaked during river crossings. Speaking of which-do not ever take your boots off when crossing a river or stream in the mountains- you will almost certainly cut your feet up.