The very second the two of you exchange vows you are, by Australian law, legally married. Saying "I do" doesn't make you married, that's why most of my ceremonies don't include those words, and saying "I now pronounce you" doesn't legal pronounce you anything. It's the moment you exchange vows.
So after then, you can do whatever you like, some people get photos, some eat meals with their guests, some just go home and eat pizza in a hotel room. But I'm guessing by "post-wedding" you want to talk about the next day, and thereafter.
The first step is to be awesome to each other. Communicate your expectations, your hopes, your dreams, and work your ass off to love one another. I recommend joint bank accounts because the research says that couples that join their finances become wealthier, more successful, and happier.
You might want to consider coming under the same family name as well. Not that names and having the same name makes you more or less married, but there's a powerful signal delivered when you use all the resources available to you to leave your old life where you weren't married and you come together under a new banner, a new tribal identifier, a new name.
This might be one of your existing last names, or a new last name you create yourselves.
Either way, communicating, joining your money and unifying your tribal identifier - name, are the three simplest ways to enter marriage with an air of success and partnership. In the end, you can do what you like, I'm not your mum. I've been given feedback that joint bank accounts aren't great for people in abusive marriages, and for those people I agree. But I could only hope you wouldn't enter into marriage with an abuser, and honestly I don't know how to square this circle. Healthy marriages are where both people are consenting, where both people are heard, both people are loved, where both people can talk about all things including money, and both people are safe. If that's not you, please seek help.
All of that said, to get a joint bank account, and to change name, you're going to need an Official Certificate of Marriage. The yellowish Certificate of Marriage that you're handed on your wedding day is lovely and formal, but it's missing that word "Official" because an OCoM can only be issued by the Births, Deaths, and Marriages department of the state of Australia where your marriage was registered, and your marriage is registered in the state in which the ceremony occured. Not the state where you live, or where the celebrant lives. Some states in Australia make this easy, some make it hard, when I'm your celebrant I'll walk you through the steps so it's easy.