Awesome!! Sounds like a blast and I can fill you in on some North Island fishing but for anything on the South then Dave would be a good resource. Also join the NZ forum http://www.flyfishingforum.co.nz/
For the north island Taupo is where you want to be or in Turangi. Both towns are trout crazy. Trout on signs, streets and just about everywhere. I've fished the Tongariro and caught a few nice lake run trout. Super nice river steeped in history. If you stay in Turangi you can stay and just walk to the river. Lots of accommodations close to the river. But so far my favorite are the smaller creeks that are between Turangi and Taupo. The Waitahanui is a beauty of a river, this is the river I caught my monster brown on(30"), it's just one sweet pool after another.You can also fish the mouth of this river shoulder to shoulder with all the others as the fish leave the lake to go upstream. Super cool to see super large fish swim by as pumice stones float past. The Hinemaiaia is another stunner of a river with lots of great holding water. Both these streams are easy to walk with great trails. I would recommend fishing on the weekdays and site see on the weekend. If you need more detailed info drop me a pm.