Well, you will need to incorporate a company, have an Operating certificate issued, write an operations manual and standard operating proceedures, produce a maintenance control manual (or whatever the N.Z. C.A.A. calls it), get hull, and liability insurance, if leasing write/get a lease agreement, if you wish to purchase the a/c you will need to finance it, you will need to find a place to hangar/maintain the a/c, hire a LAME or contract your maintenance out. There are many more, these are the ones that come to mind right off the bat.
Before you begin, make sure you are very familiar with the regs associated with the type of operation you wish to start. You might also want to find an aviation lawyer to help with the red-tape, and dealing with the C.A.A. The money you spend may help get your comany up and running sooner, and with significantly fewer problems.
It sounds like you want to lease your a/c, make very sure that you understand what the lease agreement says. Make sure it is spelled out exactly who pays for what. I think a general rule is that your lease payments cover the major timed components, but all inspections, incidentals, and premature failures are paid by you. But each lease is different, so watch out, and make sure you read and understand the agreement. I can't stress that point enough.
Good luck to you, it can be quite a challenge to get a new company up and running. In the end there are few things quite as satisfying as seeing a helicopter with your company name on it, lift off. Oh seeing cheques coming in with "pay to the order of...(your company name)" is quite good too !!
Cheers