IDP is just a translation of your license. Useless for someone from NZL.
You need to google for the official website of the Province of BC and check out their licensing and insurance regulations. All insurance there is through the province. I know that you certainly can buy & insure a car if you are on a WEV or temporary work permit. You just need the right ID and a residential address, and be able to prove residency in BC. So you may need to stay in BC for a bit to start out. Especially since you usually will only get a temporary insurance card, so you need to wait and get the permanent card in the mail (and usually it's good for one year, then you need to renew and get a new card). You need to have the card IN the vehicle - otherwise a very nasty fine.
Also you need to be well aware that there's not much free camping here -- other than crown land and the occasional WalMart parking lot, you must camp in campgrounds. And most campgrounds are shut in the winter, as are many public washrooms/info centres/other places where you can get info/shower etc. in the summer. Plus living out a van doesn't tend to work well in the winter - can be down to -30c easily. Plus you must have at least M+S tires on the van to drive any inland BC road between November and April. Preferably winter tires - and good solid winter driving experience. As well, you will find that there are few to no places in almost all ski area towns/townsites for winter camping/camping.
I'd suggest that you'd be better off staying in fixed accommodation, then renting or buying a van for summer travels. Then back to fixed accommodation for the next winter. I suspect a van, especially in the winter, will be far more expensive than renting a room or an apartment. Gas alone to keep a vehicle going and warm in the winter, plus snow tires, plus maintainance, plus insurance etc. Not cheap.