Some years ago I made a trip on NZ but including the north island.

To the south island, I will give you some tips:

- Milford Sound. A beautiful place to take a ship to see dolphins, waterfalls and a nice canyon.

- Between Haast and Queenstown, make a stop on Wanaka. It's a beautiful city on the border of the lake. Also, take the road to Queenstown crossing Cardrona and not the A6. On this road you can drink a coffe/tea/beer on the oldest NZ hotel (the Cardona Hotel). A place that easily remember the wild west movies.

- Close of Queenstown you'll find Arrowtown. It's a historical city and they have many jade shops with beautiful pieces. Also, the first bunguee-jump in the world is close of Queenstown. If you have cold blood, could be a crazy experience!

You have the option to hire a car on Wellington but pick up in Picton. NZ have a lot of "no brands" rental cars with ridiculous prices (I remember that I paid around 20 NZ$/day).

Don't sleep on Westport. The city didn't have anything (I made this mistake). One place that I can tip is the Tombstone BBH in Picton. Clean, cheap and completely different (close of a cemetery ).

Finally, if you're a fan of the LOTR, in Nelson you can find the jewellery shop that made all rings for the movies (and you can buy one too). The name is Jens Hansen and it's located on the main square.

Enjoy the trip!