Unfortunately you have chosen places that I am not really familiar with, so hopefully some other Aussies can help me out here. 1. Sounds good to me, the Great Barrier Reef is spectacular from what I hear, and it would give you a taste of many different aspects of Australia. You will get to see both urban and country Australia, and some amazing tourist hot spots like the Whitsundays. 2. Which route do you plan to travel? Going across country you would see a lot of outback, and not much else. I suggest you travel down the coast to Sydney, then cut across to either Melbourne or somewhere around Torquay (to save time, but you can go down the coast road) and travel the Great Ocean Road to Mt. Gambier, then off to Adelaide. This would probably be my choice, mostly because I am a little ignorant of the other two options, but the NSW north coast and the Great Ocean Road are spectacular. 3. I really can’t help you out with this one, WA is the only state I am yet to visit. Which country are you from? What are you looking for? Someone from Japan or Hong Kong I would encourage to visit Coober Pedy to experience the outback way of life, because the city isn’t much different for them. Someone from Egypt or the like where they have huge deserts anyway I would point to Tasmania for the forests and incredible coastlines. It all depends on what you want to get out of your visit.