10 days South Island and 10 days North Island. The rest is travel-time from and to Europe...And a stopover in Sydney.
Travelling at high season (February).......is possible without doing any bookings in advance....is possible even if you are travelling with a family. BUT ....
...You might have to do a few phonecalls at the airport for renting a car which will cost you about 55 NZ$. There are plenty of companies all listed on a board in the arrival hall (Auckland and Christchurch) and one or the other will have a car left for you. There might be no campervans available. Bigger towns always have some vacant motel units left. It can be difficult to find accomodation in the Catlins and the Westcost of South Island (Haast, Fox or Franz Josef). Make sure to arrive early in the afternoon in order to have a certain choice... or book a day in advance. (we did it only once: in Haast)
Renting a car is easiest and cheapest, at least for a family of three.
JourneyAccomodation
We loved these spacious motel units of up to three rooms which cost between 45 NZ$ (Rotorua) and 110 NZ$ (Airdale Hotel / Auckland).
Highlights were:
Airdale Hotel in Auckland / central and top quality for 110 NZ$
Boat Shed in Kaikoura / small house with private washing-machine and tumble-drier for 85 NZ$
Haylyn Park Lodge in Hahei (Coromandel) / superb view to the bay for 80 NZ$
Worst places:
Alfred Park Accomodation in Sydney / a room without private bath and window but cockroaches for 99 AU$ .........is a rip-off.
You have to decide for one or the other.....
If you like snow-capped mountains, sea animals like whales, dolphins, seals and penguins, sparsely populated landscapes and wild coasts....go to South Island
If you like maori culture, volcanic landscapes, nightlife and beaches.... go to North Island.