Thanks to all for the comments - very helpful. After reviewing all the feedback and doing some other research, it looks like Sydney(5), Port Douglas/FNQ(6), Melbourne(4) will be the plan. Dropping BNE wasn't challenging, but AYQ/Uluru was very tempting.

Question on flights - Jetstart SYD-CNS-MEL is about AU$437/US$312 per person (after Plus bundle, credit card fees, etc. - 28% higher then the "base" fare - love those LCC's). That seems like a decent price for two 3hr, 2000km flights, comparing to what I typically see in the US. Is that reasonable/close to the best I'll see, or should I wait for some type of sale?