GST registration
Mandatory once turnover hits $60K/yr. Voluntary if under.
If your business turns over (or is forecast to turn over) $60,000 in a rolling 12-month period, IRD requires you to register for GST. You can also register voluntarily under that threshold — handy if you're investing heavily in tools/vehicle and want to claim the GST back. Register via myIR or talk to your accountant.