There's likely no need to book the shorthauls within Oz/NZ now, just the 'big' ticket on AA or US. Either way the cancel & redeposit fee would be $150. Date and routing changes on AA are free as long as the destinations remain the same.

Business vs coach? Lots of opinions there. If you sleep well in coach, you'll be fine. If not, or if you want to try business class, this is a great sweet spot for it.