It's a big risk getting 100% loan. But don't forget you have the
first home buyer grant so perhaps you can use it as part of the
deposit.
Usually, if you can afford to pay 20% of the deposit, you can avoid
having to pay the so-called mortgage insurance. It cost more if you
take out 100% of the loan.
When we bought our house, we borrowed up to 95% and we had to pay
mortgage insurance. It's not too bad for us as the house is only
$200k but if you are looking something around $400k, you will be
struggling.
Also, the 100% loan is not only just the cost of the house, but the
mortgage insurance, stamp duty, (minus the first home buyer grant),
conveyancing, insurance etc. Say the house you are interested in
buying is $400k, and it could easily become a $450k - $480k loan
after adding the other costs.
So, you just need to do the Maths and compare with your rental.
Perhaps it might be worth just renting for a little bit longer and
save up the deposit and buy the house you like later. 
