You can apply for residency once you have worked here on the work visa option. Getting the skilled migrants visa is a better option In any event, as it is more flexible than working to residency, and is shorter in time. You can apply for permanent residency from this. Essential skills lasts for five years, although when here after that time you can still apply for a different visa. But skilled migrant would be a smoother option
You can travel in and out of New Zealand as often as you like until your travel conditions expire.
To travel after that, you’ll need to apply for and be granted either:
Your travel conditions will expire 5 years from the date you first arrive in New Zealand as a resident.
If you’re outside of New Zealand when your travel conditions expire, your visa will expire as well.
You will be told any travel conditions when you get your visa