JUST DO IT!
Think about it. Take a few precautions. Don't do noth'in stupid, but just go do it. It will be one of the great adventures you tell your kids about!
When I was a young fella (a long time ago!) I used to regularly do Brisbane to Clermont (1400 km ?) and back in a Mini Moke!
Don't drive at night! Be very, very wary of roadtrains. Carry a basic tool box, a few spares if your that way inclined, water, emergency fuel, swag is handy, bit of tucker, two spare tyres is a good idea, cell phone, UHF radio - even a handheld could come in handy. In a little light car like a Sirion, BE VERY CAREFUL of crappy road shoulders - they cause a lot of single vehicle accidents. If you need to pull off the seal - slow right down.
DO NOT SWERVE VIOLENTLY to avoid hitting a roo or a pig (Best bit of advice I was ever given about bush driving). Stand on the brakes to slow down as much as possible. Steer a bit left or right as indicated to miss it if possible - but don't make a violent change of direction - you are better to hit the bastard. Lots of people die trying to dodge dogs, roos etc.
SWERVE as VIOLENTLY necessary to avoid hitting cattle, horses, donkeys or camels - cause those things will kill you (lost two mates to collisions with horses on the road)!
I had the Moke fitted with a roo-bar and blew a couple of weeks wages on the biggest, meanest driving light money could buy. You could start a bushfire if you turned it on while stationary. First time I drove the Moke with it I hit a roo in broad daylight and smashed the f*cking light!
Dr 
PS: In 1977/78 I put 160,000 km on a V8 Torana in two years of bush driving. I coulda done Sydney to Kunnas in 2 days in that sucker. Fastest country road car I ever had - bitumen, dirt, mud made no difference! But man did it suck some juice! 14 miles per gallon - whats that today? 20L/100km !!!!!!!!!!!!!