I would recommend not flying YMHB-NZQN if you expect the conditions to be IFR when you get there.
Id be wanting VMC over the southern alps - at least to enjoy the view.
To depart NZ I've used Whangarie in the past - customs is nearby to the airfield so it doesn't cost that much to get them out.
Phone the two islands to make sure they have fuel. When I was coming back from NZ Norfolk island were going to drain the avgas tanks for maintenance. That would have been a long wait for fuel (days) if they didn't know I was coming.
Believe it or not they get people at Norfolk dropping in unannounced.