I have sailed from Auckland to Marlborough in Sept 2011 in our yacht, and circumnavigated the north island (clockwise) at Christmas this year starting from Marlborough Sounds. Happy to give any advice you specifically want, and happy for you to PM me. Have stopped all sorts of places along the way and worked out pretty quickly where is comfortable and whats not.
As per island time, what sort of boat and size?, how many crew have you got? have you got a timeframe to complete the trip?