Amazing show every year, the best fireworks is on the harbour bridge, best locations to view are at northern foyer of Opera House or Kirribilli.
Luna Park has closeup view, entertainment, rides, reasonably priced, but looking at the back of the bridge, not ideal.
Buy the expensive tickets to watch in comfort, tickets from opera house, restaurants/bars next to opera house, commercial boats with license to stop close to the bridge, or ferry boats.
Tips for other travellers
All public transport may not be available till 1-2am, organise your return journey or you may not be home till 3am
view from Kirribilli