Not a problem, I have learnt a lot from this forum but I have little to add so I can only chip in every now and then. Its all about helping isn't it?!
I am not sure about the great barrier reef as I have never been there but nearly everyone I have spoken to about it raves about the beauty. As for the rock (AYR) I am tempted to say that 1.5 days is 1 day longer than wanted but that would be harsh. I am assuming that you are going to see sunset and/or sunrise. There is little else to do there.
Travelling in October/November the weather should as least be nice for you, at least warmer that Canada.
Again this is only me, but a few days in tropical QLD (Queensland) at the great barrier reef followed by a day in Mel sounds great.