After you renew your NZ passport, you may enter NZ and live there with no further paperwork required.
Based on what you've said about your age, you would be eligible for New Zealand Superannuation at age 65 (since you lived in NZ for 7 years already after age 20, and you need 10 years before age 65). That's the current rules - note that there are proposed changes to NZ Super which would affect your eligibility if the rules are changed:
In another major policy change, immigrants will have to live in New Zealand for twice as long - 20 years - to get access to NZ Super, including five years after they turn 50. It would apply as soon as the law changed - next year if National remains in power.
For your Swiss pension, New Zealand does not have a Social Security Agreement with Switzerland. You will probably need to contact a financial professional (or Work and Income directly) to find out more about your individual circumstances.
Anyway, as always with moving countries, there will be a bunch of work involved in moving your finances and belongings from one country to another. However, once you have your NZ passport then there will be no further work from an immigration perspective.