Obviously, I’d not be selling units that are less than 12 months old, since they probably get double the capital gains tax.
Given that you’ll be earning less in future, I’d be selling the units with the highest cost base, to reduce your current tax, unless you end up carrying your capital losses into further financial years. It may be that you’re never going to use those capital losses to offset capital gains.
However, this gets to the question of what you intend to do with your investments in the future. You may intend to keep them and live off the dividends and earnings. You may intend to sell them all gradually, and add them to your superannuation (doing this gradually could keep you under the tax threshold each year, and be more tax efficient). As you will have NZ residency, you may want to sell gradually, and add to the NZ equivalent. You probably need advice from someone with experience in both systems.