Hey Joker,
I was in TW for a couple of years and spent time assessing the Flight Screening candidates.
The basic purpose of the Flight Screening process is assess your potential ability to fly (IAW military protocol and processes) and to assess your potential as an officer. The flying on the CT4 and CAP10 is looking to see that you can follow instruction, learn from mistakes and develop capability over a number of sorties. The hot tip here is to listen to the QFI and accurately apply what you are asked to do, study hard at night to ensure you know all relevant attitudes, powers, techniques and generally show confidence yet humility.
The board interview will assess your leadership potential and motivation. Know the RAAF leaders, the SQNs, a/c types etc. What a/c do you want to fly and why. Read the paper and know current affairs relating to the RAAF (C17, Iraq deployment, etc). Have a think about why you want to join, how will you feel if sent on operations, time away from home on often tough conditions, your apporoach to command etc. The board assessment again is looking for guys/girls that have potential, intelligence, a motivated attitude, an understanding of your chosen career and generally will fit in. The common yardstick asked by the board is " Can I sit next to this person for 10 hours, and trust his/her abilities in war".
To answer your specific questions, I would suggest that an aerobatic flight may be of some slight advantage, at least to give you a feel for the environment. However, if money is tight, dont worry about it. The cousre is aimed at people with minimal to no experience.
As for secondary duties, there are numerous as mentioned. To add to the list, also include Crew Resource Management facilitator, Aviation Risk Management facilitator (the RAAF had recently become very AVRM aware), Information Systems co-ordinator (you look after the sqns database etc), publications officer, programmer (programs the sim and flying), Public relations contact etc. The list goes on forever. Be aware that flying is only a part of your role. You play a part in running the squadron.
Bottom line - show humility, motivation, a willingness to learn from staff and from mistakes, a hard working attitude, be prepared. Most importantly, be yourself. We look very closely for honesty and integrity.
Hope this helps and good luck.