Travelling in NZ???

[v15ben]

I have decided the basic route for South Island but I am not really sure how long to spend in each place. I have the Lonely planet guide book for Aus and NZ but that isn't really helping decide on timings a great deal!

The route around South Island will be roughly this one:
Fly into Christchurch
Couple of days in ChCh
Then a day at Akaroa
The ChCh to Queenstown, Wanaka and Mt Aspiring National Park
Next up Doubtful Sound and Milford Sound (a day each?)
Mount Cook (day or two)
Hokikita
Franz Josef Glacier
On to Greymouth and Transalpine (3-4 days up to Nelson?)
then Nelson.

North Island
The plan is then to fly Nelson to Wellington with Origin Pacific using my ISIC card, or to go up to Picton and take the ferry across Marlborough Sound, the ferry is looking favourite on this!
Wellington for a day or two
then on to Taupo
Rotoura
Wiatomo
Auckland for a couple of days at least
and if there is time left
Bay of Islands then back to Auckland to fly back to Sydney then home!

I have roughly 5-6 weeks (if exam dates work out) to spend in NZ following a 2-2.5 week trip up the east coast of Australia so how long would you suggest at each place.
Also, where are the places that it is worth spending a day, looking and enjoying then moving on, rather than spending a long time there and getting bored (e.g. Doubtful?)

Fire away folks, thanks!

[v15ben]

Thanks for the replies:
I have had a look at where I would really like to go in my 6 weeks and have come up with a total of about 38-40 days of travel. This is a top end estimate with 4 days in Auckland, 3 in Queenstown, 3 in Wellington etc etc so I could do everything easily in the time I have available - or at least I hope so!