Hi Ping,
Welcome to the Wellington end of NZW. If you haven't already you might want to visit nodedb.com and register your node there. I'm pretty sure that there is at least one other person out that way, if not more. I'm in Strathmore so I'm not sure we would get any line of sight between us.

Antennas - depends on what you are trying to do. Being a node attaching to somebody else may need a grid dish or similar. Being an access point for others will need something like the slotted waveguide design.

Let me know if I can be of any help, either via the forum here or the mailing list.

Cheers - Colin.