To expand on freeride_addict’s suggestion, I’d suggest basing yourself in either
Rotorua or
North South Island or
South South Island
Rotovegas for endless bike park with a natural feel in parts
Nelson for the Hira MTB park (supplejack, R&R, heaps) er, the other bike park (with Broken Axe, Maitai Face), Codgers for lots of blue trails, Coppermine, backcountry (Starveal (sp ??), Fishtail, and then epic backcountry in Marlborough (Nydia ?Bay, Whites Bay, Wakamarina*). The best bike park in NZ is nearby but is privately owned so unless you have an entry to the DME you won’t be able to ride there!
QT for bike parks in Queenstown, Coronet Peak, Wanaka and you could push up towards the Backcountry riding in Canterbury (Mt Oxford, Mt Thomas & Richardson (Blowhard)).
I’m getting a bit misty eyed actually 😐