Q: thinkin of buying a bike to ride the outside when i get there ?
A: In practical terms, it will take you four days of solid driving, assuming you stop over night. Perhaps 3 if you can share the driving with someone else. I would recommend a more leisurely pace and taking time to smell the desert roses if you can. And it is possible to drive all the way from Sydney to Perth on sealed roads, and in fact on fairly major highways. While a 4WD is probably a good idea, its certainly not essential. The Eyre Highway across the Nullarbor is remote but it also a major truck route, so if you break down it will be extremely inconvenient but certainly not life threatening. But I would still recommend having some extra water and food in the car, and taking the most reliable vehicle you can find so as to avoid the threat of breaking down. Of course, if you intend to take routes other than the highway, then all bets are off and you better be very well prepared.