Brisbane is on the central East Coast of Australia and not North of Australia.
You need to go to Western Australia to swim in the Indian Ocean as the ocean near Brisbane is the Pacific. You should really fly into Cairns as the Great Barrier Reef is just off Cairns.
Don't call a Koala a bear in Australia as you will be told they are not a bear but a marsupial.
I was there in their winter time and it was really nice weather,just like summer in Britain and Ireland. It may be a bit chilly at night but just take a few long sleeved tops and you will be fine.
Perhaps you should do a little more research yourself. This site should have all the info you need to plan your trip as it is the official tourism site.
http://www.australia.com/