It's true that insurance is not compulsory (personally I think that's ridiculous!). When you pay your vehicle registration you are covered for third party medical expenses, but not for the cost of any damage to vehicles so definitely worth getting at least third party insurance, which is all I have (as my three cars are all 10 years old!)
I found SGIO cheaper than RAC and HBF for insurance and they give you a discount if you have multiple policies (home and contents or more than 1 vehicle). I do have 60% NCB and each policy is less than $150 per year. Fortunately I've never had to make a claim on the car insurance but I did on the house insurance last year (fence blew down in a winter storm) and they were really good.
Regarding real estate, there are plenty of places available now compared to a couple of years ago and the prices have dropped too. If you see a place has been available for a while, don't hesitate to make an offer. A friend of mine done this recently and saved 10% or about $2000 over the course of a year, not bad for just asking the question!
If your looking for short term accommodation try ozhouserental.com (you can check them out on Facebook too) I know a few people that have used them and were really happy. You probably still have to have police clearance etc but deal directly with the homeowner which cuts out a lot of the red tape of dealing with real estate agents. If you're a single guy/girl flying over to try and get organised before the family join you and don't mind sharing for a bit, look at flatmates.com for a cheaper option.
For short term car rental I often use car rental.com when travelling over east, but my friend just told me about a company called "hot wire" which was cheaper still. She hired a car this week for 4 days , unlimited mileage, for $15 a day!!!
Hope this was helpful