I've been to NZ 4 times and done all the tourists haunts on North and South Island, the distances are not too great but the travelling times can be extensive as mainly on country roads. Get as many tourist holiday brochures/web sites as you can to identify key locations you may want to visit, then the unexpected scenery hits your on your travels eg we stayed at the Hotel Hermitage Mount Cook, where from the dining room during your evening meal the view of the snow capped Mount Cook turned from white to pink in the setting sun
https://www.hermitage.co.nz/ absolutely breathtaking.
If you go to Queenstown you have to do the gondola's and Luge (lots of images on line, and a breath taking experience) of course also visit Hackett's bungee jump. So many great locations and unusual and unexpected stops eg on way to coast from Wanaka stopped for breakfast at a small cafe in the middle of no where and enjoyed really great food, all around the walls were pictures of the fishing exploits of the owners family, the most noted was the largest Great White caught on rod and reel, just a few miles down the road. You can spend hours in conversation from a very welcoming people.
Some of the roads are gravel tracks eg 90 miles beach and parts of the Coromandel and therefore hire cars hadn't used to be allowed to to use those roads as stone chip damage can be extensive, tourist buses often spraying you with stones in their haste to get to their destination. The scenic railways also offer a slightly different prospective and allow you time to enjoy the scenery and take the pressure off having to drive everywhere .Places like Milford Sound can be a demanding drive to complete in a day.
I found in all my travels to NZ I used to hire the cheapest car (highest demand) and then upgrade to the most expensive available at the hire desk and usually you can drive a good deal, but there is a risk at peak times of limited choice. Most fun I had was in a 5L V8 Ford Falcon, had to run it in, amazingly economical and went like a scolded cat.
My favourite hotel in Auckland (from nearly 20 years ago so things may have changed) was City Life on the main Queens Street close to the harbour and railways station. Some of the best sushi I've had has been in NZ..........you get it absolutely everywhere.
