Go for sole trader to start with. It's really easy and doesn't cost anything. Just be aware you are personally liable for any errors. For example - if you made a repair and broke someone's device they could take you personally to the disputes tribunal. If it was a company it would be the company in dispute.
Normally not a big deal unless you are talking big bucks.
As for import duties it really only gets interesting if you import more than $400 worth at once - if it's less than that then dont worry. I seem to remember there is an 'import bible' that has all the import codes for items and subsequent duty cost. And yea - a broker would have access to one of those.
From memory I've got a spare copy of the NZ importers handbook(diff to the bible). Drop me an email at
[Edited to remove email address in line with Forum Rule 10. nigee, make five posts on any thread, then you will be able to use the site's PMing system, after it automatically switches on after about 20 minutes from your fifth post.] and I'll send you some more info.
Just make a start on your biz. Have faith you will figure it out as you go.