I also planned to go to NZ with my 3 years old kid on 30 Sept for 2 weeks.
We planned to drive ourselves from Queentown to Auckland (we have 7 passengers and 5 of us have driving licence). Yes, the driving is very long, the longest driving per day I planned is 5.5 hours. I had a rough itineary in excel file, if you want, you may leave me your email address and I can email it to you. For things to do, I guess beside scenery there must be lots of activities and I need to find out from their tourist information center when I arrived there.
You may also find the following website useful:
www. newzealand.com