There are three stages of interviews.
At the OSB (third stage) the interviewers ask questions ABOUT YOU to clarify things that make their noses twitch, such as the possibility you of failing English in the HSC (there's a minimum English HSC performance band for eligibility into ADFA); or medical conditions such as degrading vision, asthma; or your past criminal record of sexual harrassment etc.
The Assessment Day (second stage) is where the questions all revolve around knowledge about the DF (Superannuation, bases around Aus, current operations, leave entitlements, fitness test specifics, salary, the chain of command, ADFA daily routine, RMC-D daily routine, ADFA military training specs, RMC-D Class specs, etc) as well as why you want in (your motivation, your attitude to life, the impact on your family, your willingness to put yourself in harm's way).
My answer to that question was: "I would not hesistate to take another person's life if that person's purpose is to take the lives of my comrades, of my friends, whose purpose, in contrast, is to serve to protect the lives of civilians who deserve to live without fear and intimidation."
By the way the "killing a man" question was asked during the JOES (first stage), and rightly so. No point letting a person progress in the DF recruitment process if he refuses kill.
I think there's 3-4 recruitment processes spread over any given year. So just call up, create a profile, and book yourself in for an interview.
It depends on how low. If it's only a little bit, they won't care all that much. If you're a youth you can apply for medical wavers if you fail any minimum medical requirements by a little bit.
You don't necessarily have to be strong. Fitness is first priority. Fighting is all about technique anyway, not how macho you are.
Although the fitness test is a pushover, once you get into 2nd year (?) at ADFA you'll be required to do 100 situps, 50 pushups, a march for a long distance, and a timed run with a 50+kg backpack on.
?= not certain about, writing from memory of what I memorized back in late '04