With Parengarenga Harbour I hear you need to go to a local to get the keys to be able to launch? Do people know anything about this? I hear the fishing in the harbour is mainly sight fishing. Should I be starting by fishing the edges of the sand banks?

Any advice would be appreciated 

Access you are talking about is probably at Paua. One of the local stores hold the key I think. We found snapper fishing good around the mouth and had some good spots up the southern channel that worked when the mouth wasn't, so don't be afraid to fish up the harbour, but watch the tides. Lots of big Trevs if you target them, and heaps of Tope that will annoy the hell out of you. SWF on the flats is a good possibility and there are spots on the northern tip of the southern head that are great for Trevs. Overall though, a great place to explore and fish. If you can get out over the bar (be careful) there are lots of patches of foul in ~20 - 40m between there and North Cape. Good big snapper country if you can find the foul and explore around. Do not burley as there are also plenty of sharks. Also more foul south of the harbour entrance, but maybe a bit harder to find unless you know the area.

 The Ranganunu (Awanui) harbour would be well worth your time also.

You wont mate...only special people get onto great expedition.   don't see the point in going up there anyway, fishing is over rated and loads of thieves