costa:
1) you should start looking at the methods course now. as good as the pathway might sound, packing in the whole methods course is NOT a good idea. I'm sure you are self-conscious that mathematics is not your strong point, and believe me that any normal person can only do a certain amount of math in a given amount of time. Considering that you have already sat through the coursework last year, it might be an idea to just go over the course again, maybe with a tutor, and cover the main concepts before you start this bridging/foundation course [or alternatively, start now]
2) don't put all your eggs into one basket. I'm not sure about requirements for commerce at RMIT/Deakin/La Trobe/ACU, but they are certainly viable options you should look into. Apply from VTAC first, and after you have accepted the first-round offers, try for a second-round irregular placement at Monash/UoM. That way, if they reject you, you always have a course to go into. If you apply for irregular offer straight away, I am fairly sure you forfeit your application via VTAC.