I've just started researching this too.

It's very hard to find information online as this is fairly new territory for all.

There was a news article on stuff or NZ herald recently that talked about IRD treating crypto like gold bullion.

Here is a similar article publish on NBR recently
https://www.nbr.co.nz/article/ird-may-treat-crypto-currencies-gold-held-profit-wont-comment-bitcoinica-b-211510.

and of course you can read the gold bullion PDF document on IRD website
http://www.ird.govt.nz/resources/6/e/6ec89340-3f88-446f-90da-f50aaae363c9/QB17008.pdf

These are helpful.

It would be good to know what the implications are if you wanted to sell part of your portfolio say 10% to convert back into NZD. A lot of examples I've seen are similar to the above example showing buying at a set price then selling the whole investment for a higher price.

I think this is relevant for users who got in before the big bull run and (for example) invested NZD1000 into BTC. The investment grew to NZD10000 so, still wanting to hold a position in BTC, they take out NZD1000 so the original investment is now off the table leaving them with an investment value of NZD9000.

Another complication to add would be if you had bought the original NZD1000 in installments (on different dates) so the BTC price varied when you bought.

Interesting stuff. Would love to hear how people get on into the future. I guess someone will have to be the test case haha.