I've had no experience with campervans but if your hiring for ten weeks, perhaps it would be cheaper to buy one and then sell before you leave, if thats a viable optio for you.
Alice Spings/Ayers rock has decent roads into it i'd expect, best to go to a map store to find out, get a touring atlas of Oz. Its the 'roads less travelled' that get rough, the touristy places should be fine (seen buses parked near ayers :wink: ) but its a flaming LONG LONG drive. To give you a rough idea, Sydneym to Ayers rock is about 32Hrs drive, NO stopping. 2823 Kilometres
I drove to condobolin, 8 hours drive, and as the bird fly's on a map i wasnt even 1/4 the way to Ayers
But with 6 months, I think you could do it all. I'd go Sydney - Melbourne - along south coast then to Alice - then through outback QLD to Northern QLD, and then follow the east coast down to sydney
You cover pretty much everything worth seeing bar Perth and Darwin (dont tell Scolers, but perth's not really worth seeing anyway :wink:
Hope some of this helps