Usually, flights from Oz land at T3 but like myrm said, there may be occasions where the plane lands at T2. You will only know this info about 2 hours before you land. Info will be reflected on your IFE screen on board.
Terminal transfer is trivial. Take the airside skytrain and it will take at most 10 minutes, depending on where your arrival/daperture gates are, including walking and waiting time at the skytrain station.