There are three different ways of working as a sex worker/escort in New Zealand or setting up a business. You can either work privately on your own, work for an owner of a brothel or In a SOOB (small owner operated business). 

A SOOB is upto four sex workers working together with no boss, in a SOOB no one is in charge of another sex worker each person is in control of there own earnings and you do not need an operators license for this buinsess.

Privately you can work for yourself from home or somewhere else and you don’t need a license to do this.

Working in a business/brothel or escort agency the operator of the brothel has to have a special license and must make sure the workers are over 18 and use protection and are looked after. Workers sign contract agreements under independent contractors instead of employees which help with your rights while working in the business. 

Here is a link to the justice site to apply for a certificate https://www.justice.govt.nz/licences-certificates/brothel-operator-certification/apply-for-a-brothel-operator-certificate/

If you are looking to go private and work alone from home or a hotel/motel you need to contact your local council, as they have made rules in certain residential areas to not allow sex work and they can help tell you where it is allowed. If you are working from your home check your tenancy agreement as it might say you cannot work from your home. 

When it comes to paying taxes and all the other legalities of the business it is best to contact a good account and lawyer.