To answer question 4, Air NZ is going for the 737-800. It is going to replace the entire fleet, both the 737-300 and the A320.
It is a easier aircraft to turn in places like Norfolk and Nuie where they dont have the equipment to accept baggage tins. The 737 sits a lot lower than the A320.
And no doubt Boeing is offer a rather sweet deal on them due to the delayed 787.
Will make sense to have the same aircraft across the fleet, in situations where there has been large delays due to a aircraft being U/S and having to wait for a aircraft to return from across the pacific. This way they can pull one from a domestic route and cut the delay times.