Been there, done that. A few points.
1) If you must pay up front, check that the school use an ESCROW (i think) account. It's basically a bank account that holds all you dosh, however, the school can only access the funds after you have flown. So if they go under, you're money is safe.
2) Sort your medical out before travelling out there. You can't do a Class 1 initial outside of NZ, however, there are a few AME's in the UK who do NZ renewals and they will be able to tell you whether or not you will have any problems getting an initial class 1.
3) Don't bank on trying to get work out there afterwards. A paying job in NZ is like rocking horse poop.
4) As you know, you'll need a visa to study there. However, if you are under 30, you're probably better to try and get a working visa for a year. This should allow you to study and also earn a few extra cents in the evening.