Alec,
I think the main thrust of advice you're likely get won't cite books and theory at all. Rather, be clear about what the RAAF is about, it's philosophy, it's sphere of ops, the variety of roles and aircraft etc. Further, you will need to impress with your knowledge of current world affairs generally, but specifically how they might touch on Oz's world views and aspirations. Do you know the various political parties' views on defence? What's your view on their view? Novels are of limited use for all this, I'd say, and if you get in, it'll be a good old while before anyone is quizzing you on fighter combat tactics.
Best of luck.
CG