Zanzibar138 has answered this well. I agree fly into Sydney stay a few days and see the big sights like opera house, bridge, take a day trip to blue mountains, depending on time of year take a cruise even a
Disney cruise. But don’t stay too long in capital cities as the best things are more natural and you want to be outside.
The Olympics are in Queensland so that takes you closer to Great Barrier Reef, but know that it is not close to Brisbane, in fact if you come up from Sydney it is only about half way. So recommend a few nights in cairns or even better port Douglas and day trip out to the reef - if this is a once in a lifetime trip to Aus don’t miss the reef.
If you live in a hot place, annd want something different annd cold, and love bush walking and all things nature then recommend coming to Tasmania. There are spectacular bush walks here. We also have Mona (art) and Salamanca Market (world class market) and if you like fish n chips tasmania has the best in the world.
Where are the best fish n chips in USA?