OP here - thanks all! Was just looking for ideas/suggestions, so I can start researching! I've gotten plenty of pointers, thanks!

We did a two week trip in late August early September which of course is not summer there. We flew from DC to LA to Sydney. We spent 4 days getting adjusted to the time different - really enjoyed seeing the sights - Gardens, Sydney Bay Bridge, Opera House etc. Because we were with a 4 year old we also did the zoo, and other kid friendly activities. It was great weather - chilly autumn feel so we didn't do any beaches. From there we flew to Tasmania. Loved it! There was snow in the higher elevations. We rented a car went out to some of the islands and enjoyed it a lot - hiking, outdoor activities we were there another 4 days. From there we flew to Adelaide - more sight seeing. Then back to Sydney for a day and half. There was so much to do - with a 4 year old we were limited. My DH really wanted the great barrier reef but due to time of year and age of our DS we decided it wasn't going to be the time to try it out. Enjoy!

What does "high level" mean?

Perth is indeed lovely, but if OP's original question is the equivalent of "Flying to Boston! What to do in the US!" the Perth is "San Diego!"

Perth is far away, and expensive.