On Holiday, eh? You lucky blokes!
That is a really nice area. I visited near there several years ago and still remember the good time. I was in the area "next door" so to speak, and went from Picton to Wellington along the ferry route. The ferry at that time left Picton around noon to the early afternoon and I managed to hitch-hike on a fellows new boat. The crew was in the pub and he wanted to have a sober hand on-board to help sail her.
The trip across Cooks Strait was a ride in quite strong winds and fairly good sized seas and whitecaps. Got into Wellington sometime around 10pm and it was dark.
As for suggestions? I'd say, put yourself together a translation dictionary. Maybe you can search for something like that on the Internet. Then maybe try to tune in some Kiwi radio or TV stations on the Internet and listen to their "English". This way when you try to communicate to them it'll be a lot easier.
The terrain along the route we went was similar to that of the Pacific Northwest and somewhat like the outer BC central coast. Mountainous but not as much as the mainland BC coast and well timbered.
Driving a car: If you rent a car be very, VERY careful. I assume they still drive on the "other side" of the road. One problem I had was when making a left turn in front of a lot of oncoming traffic, because it was quick to get out of their way, I found myself on the "wrong" side of the road I was entering. Fortunately the drivers coming toward me had loud horns on their cars and warned me of my error. Do this once and if you survive and you should be a much more careful driver afterwards.
Pedestrian crossings: be sure to look "the other way" before stepping off the curb. Same situation as above only this time you won't have steel to protect you.
Hope this helps a little bit. By any chance you wouldn't happen to want a guide, would you???