If you go in visa-free for the 90 days then you must have an onward ticket. You can get an dummy ticket or a refundable ticket if you aren’t sure of your departure date or location yet. Several people on this forum have used onward travel ticket services as a placeholder for an actual ticket, including me.
If you apply for the visa, you can get up to 6 months and you do not have to have a return ticket. I discovered this the last time I went in. The visa is free but doe require some time filling out the form online.
Most of the sits we did in New Zealand were through Kiwi HS. There just wasn’t enough on Trusted. We also spent a fair amount on accommodation, as there weren’t always sits where we wanted to visit, but it is possible to find more affordable accommodation if you are driving. I posted a blog further up in this post that talks a bit about buying and selling a car in NZ. I highly recommend it. (Also we took the Picton ferry and it was great, but a few weeks later it was delayed for thousands of people, so it’s definitely hit or miss!)