Well done on finding this site, it will help you.

So, you don't actually need an agent for the application process, i have personally known 4 different expats and families to go over without using one.
They are quite expensive. But,

If you do use one, they will ensure that all paperwork etc is done properly and this in turn will lessen the likelihood of any delays due to wrongly applied or filled out forms etc.

Sorry i can't be more specific help, i am sure someone will be along soon (or overnight if they are in Oz!) that can give you more info and advice on selecting a suitable agent should you choose to go this way.

Good luck.