Australia is absolutely massive, its almost impossible to see everything in one trip. We decided to stick to the East Coast as we only had 3 weeks and a limited budget.
From there we took the Greyhound bus the rest of the way, stopping along the way.
We spent 2 nights in Byron Bay, 3 nights in Coffs Harbour, 2 nights in Port Macquarie where we visited the Koala Hospital and then 3 nights in Newcastle. Our final stop was Sydney, where we spent 3 nights.
Our itinerary was perfect for what we wanted, we really enjoyed Australia and felt like we saw absolutely loads in our short time there.