The Suggested Route

So far all that is set in stone is that im landing in Perth on 27th August next year. I roughly know that I intend to make my way to Adelaide, then Melbourne, two or so weeks in Sydney then head up the east coast. Anyone done this? Any hidden gems along the way thats worth a look? An experience I shouldnt miss when visiting any of these places? Let me know guys as I want to try everything once and see everything possible!