Added a few things.
I would recommend for a year 12 leaver to begin with the Cert III in Business and then continue with the Cert IV in Business Administration, particularly if you are not in a supervisory role in your workplace/volunteer organization etc. The Cert III in Business is still valued by employers as it has modules which are not included in the Cert IV.
Please note:
The Diploma of Management is quite a prestigious degree/qualification, and therefore it is generally made available to those who are in a supervisory roles in their workplace, therefore if you currently do not have a job, it is ideal for you to take the Cert III in Business followed by the Cert IV in Business Administration. The application process for the Diploma of Management may also be subject to an additional interview. If you have any questions as to what constitutes a 'supervisory role' just ask.
Most people eligible for the Diploma of Management would probably be in university and have been in the workplace (though some high schoolers who have been working for a while may be eligible).
The Certificates are generally seen as an additional factor to getting employed/standing out in your current workplace, and the Dip. Man is generally to do with standing out in your current workplace / moving onto bigger things.
Will this interfere with the criteria set out by the Monash University Faculty of Medicine?
No, the faculty of medicine states that you either have to be a year 12 completing VCE, or someone who has completed VCE in the last two years and has not begun any tertiary qualifications. You will be allowed to undertake the Monash MBBS if you have a Cert III or Cert IV.