The new law has done away with the difference between 'visa' and 'permit' which used to exist. Now, they grant a visa, which allows a person BOTH to travel to NZ, AND to live there (for whatever specific purpose).
While within NZ and within the terms of your visa, you are legally resident and don't need to renew anything. As you are intending to leave settling in NZ till late in the run of your two years' travel conditions, you would probably only be eligible to renew for fourteen days in the first instance. This is the page that deals with all that aspect of things.
http://www.immigration.govt.nz/migra...quirements.htm It is exactly how things used to be with RRV and IRRV, just different names. The way you are choosing to do things, you will have to expect that you won't have the legal right to go out of the country for very long, and come back freely, until you have lived there on a settled basis for long enough to prove your intentions in official eyes.