A mortgage broker can help you find a home loan when you are looking to purchase a new house. A mortgage broker can find you loans from multiple lenders to hopefully find one that meets your needs.
Some mortgage brokers may only deal with certain lenders, you will want to investigate your options yourself to make sure you are getting a good loan.
Yes, commissions are generally how a mortgage broker makes their money.
Most mortgages in Australia are from 25 to 30 year loan terms.
This number will vary greatly depending on many factors, you can check with a mortgage broker and they should be able to give you an idea of how much you can borrow. There are also online mortgage calculators that can give you a very rough idea of your borrowing capacity.