Pete,
The two important things in Australian golf (from a GCA perspective) are the Barnbougle complex and the Melbourne Sandbelt. I'd have a really good look around these, and then if you have time left over, pick from the joys of NSWGC, Newcastle GC, Royal Adelaide, Royal Qld, Lake K, St Andrews Beach, The National etc, according to which other parts of the country you'd like to see.
Barnbougle's easy: you play both courses.
On the Sandbelt, I'd play a variety of courses to get a feel for the style and the variations within it. Within this context, play Victoria, Woodlands and Metro. Victoria isn't my favorite course, but it's challenging and located across the road from RM, so you can see different ways to use pretty similar pieces of land. It's also a great place to stay - handsome old clubhouse; located in centre of the Sandbelt. Obviously you must play RM & KH. Commonwealth, Yarra Yarra & Peninsula are (lovable) optional extras.