New Zealand is a small country that drives like a big one. Fiords, volcanoes, a wine valley, a glacier, and a city you will leave quickly because the rest of it is the point. The South Island is the screensaver. The North Island is steam, surf and a culture that is not a museum exhibit.
You will rent a car. You will underestimate how long a 'three-hour' drive takes on a winding two-lane road. You will stop anyway, because the shoulder looks like a national park. That is the correct itinerary.
Summer is long evenings and booked-out huts. Winter is ski fields and a Queenstown that still knows how to have a night. Shoulder seasons are the sweet spot if you can be flexible with weather.
Take the Māori names seriously, clean your boots for biosecurity, and leave the place as empty as you found it. New Zealand has heard every 'middle-earth' joke. It is better than the joke.