Everyone is different. Who pays for what may be decided by your heritage, family circumstances, as well as your finances. History may mean your family is willing to pay a certain budget, or for certain items. If your sister had so much, you may expect the same. It's very important to plan your budget right from the start. This way you don't blow the budget before you have decided each element.
If you really want to follow Australian tradition the following is an excerpt from 'The Penguin Book of Etiquette' by Marion Von Adlerstein.