Travel around New Zeland and Australia

hi:
I would like to make a trip around New Zeland and Australia.
I am from Spain. I am looking for flight companies go to Auckland from
Spain, but I want to make an stop-over in Australia. I want to stay in
Sidney and Camberra for 3 or 4 days (using the same ticket to go to
New Zeland). Is it possible? I have heard it is possible with an
malasian airlain company.
When I arrive to Auckland I want to rent a campervan (spirit 2 or
something similar) for two people.
What is your recommendation???
How much is the pass from north island to south island? in which
companies? (if there are more than one)
Thanks on advance
Matías
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