Tom,
The RAAF will be very interested in your academic ability when it comes to TP postings. I am presuming that your school results are fine.. if they are not, then you are going to find any serious test flying a bit in the hard basket ... it is a mind skills game more than just stick and rudder skills.
Why don't you do the sensible thing and go through ADFA ? ... do a BTech (sort of a three year cut down Aero Eng degree and, from my observations, not a walk in the park by any means), wings course (and if you scrub off wings course they put you back to finish off the Aero degree before going into an engineering posting), some operational flying and then, with a bit of luck, pick up a TP course and a posting to ARDU.
ADFA is a solid period of training and, for most, a real big culture shock... but if you survive it, you have a very wide range of career options available.
Whichever way you go, best of luck.