Originally Posted by Crocodile

My geography may not be great, but the Great Ocean Road is west of Melbourne and Sydney is north. So you can drive the GOR, but it is not on the way to Sydney.

Personally, I would not drive from Sydney to Melbourne - is a lot cheaper, easier and safer to fly. There is plenty to do around Melbourne, including the Yarra Valley wine district (stay at a nice B&B there?) and a two or three day trip along the GOR would be recommended - maybe a night or two at Lorne (although, this is a very popular beachside town for holidays).

Book it all yourself, no need for an agent. Most hire cars are automatics, just make sure you get one with a sat-nav. Weatherwise, Melbourne can be very hot at that time of year (40C+), but it is not unheard of to have cold weather also during the day (sub 20C), so you will need to bring jackets.