Hola, we are a young couple from New Zealand moving to Spain in about 6 months.
We want to buy a car or van immediately and travel around for possibly several months before
choosing somewhere to settle.

Is it possible to obtain an NIE number without a permanent address?
And can you then buy a car (probably from a dealer) without having an address..?

Any help is much appreciated!

Any advice on which makes & models of cars are the best also much appreciated!

Legally and officially speaking No and No.

But we obtain NIEs for people when they are buying a property but before they have decided what to buy and consequently they dont have an address - and given you can apply for NIEs in other countries and dont have to be resident for NIE many people dont actually have one at application time.

The car has to be registered to the owners address - probably the dealers know a way around that - buy hey why buy and have the complications? Why not negotiate a long term rent and then both problems go away. Including getting rid of it when you are going home.