Using an agent is the applicant's prerogative.  At the end of the day, what counts is how efficient the job is done.  Australian migration requires a lot of research, experience, dedication, determination, patience, and most importantly money.  Some may have done it by themselves.  Testing the water so to speak, and took them a year or so to obtain approval after some trial and error.  Good exercise though to gain experience and know how involving Australian migration.  Some are still in the pipeline awaiting decision.  DIBP website gives the general view of a particular subclass, but never the full context and explanation to each regulations, sections and clauses.
  
Your career pathway should be vertically aligned.  Choosing a course should be based on your most recent course taken and the nature of your current job.  Why? (1) So you will get approval for the student visa you are taking.  Education providers will admit you in their institution.  That's what they do to obtain students.  Although you are able to obtain COE, when it comes to visa assessment you may be refused because the department cannot justify the reason why you are taking the course.  That casts doubt on the application.  (2) To obtain additional points if decided to do a General Skilled Migration.  Everything you declared on your application will be accounted for and will be used in assessing future application.  Engaging in odds jobs is okay, but when it comes to migration not all can be counted.
Piece of advice, please don't just chew on what others are telling you to do.  Some migration advice may get you to Australia, but may not lead to migration or permanent residency.  In other words, there is no clear pathway for you.  It's like studying your battleground before engaging into a war.  What is the sense of taking the advice if it will lead you nowhere? It could be a waste of time, effort, and money.  Over the years, I've witnessed some suffered from depression because of a wrong advice.   Some were asked to do a bachelor degree in Australia, though they do not have to.  Some were asked to take on a diploma or certificate courses which will not lead to getting registered in Australia.  Be conscious and cautious.  GOD BLESS ๐