From Cairns to Sydney in 12 days

Hi Fellow Travellers!

Could anyone who knows well the East coast advise on a reasonable itinerary to see some of the ' must' on the East coast of Australia. We are using public transport also taking internal flights. And travelling in January. This what i am considering so far:

1. Cairns & day trips to see the Great Barrier Reef( 3 days)

***Any place to break up the journey down to Airlie which can add something unique to our trip?. We are interesred in country music, Koalas, outback gold towns without going too far from the coast, any chance of seeing any of squeeze any of these between Cairns and Airlie Beach?

1. Airlie Beach & Whitsunday Islands ( 3 days)
   ***which islands are the most impressive ones in Whitsundays?

*** Any suggestions of how to continue the trip from here? We can fly to Sydney from Airlie Island if there is something appeling instead of going down to Brisbane

1. Maybe Brisbane? and flight to Sydney?

2. Sydney

Cheers!