I would agree with all that has been said already!
Take your working visa and head for a city, and then stay until you feel ready to move on....just make sure you do!
Nb. The aussie summer holidays are during the UK christmas break, so jobs in some cities are harder to come by at certain times of the year - just as they are in the UK. If you are going to work in a bar or restaurant serving drinks, you will need to get your RSA and RGS if they have pokey machines or any sort of gambling. These courses are easy to pass and usually take 1 day, but all the same you will need them if you are planning on bar work - most bars in australia have pokey machines. Courses take place periodically in all cities and they will cost around £60-100ish.
Unless you want to explore the country from Mel-Syd I would recommend the taking the XPT rather than the bus if time is an issue. The XPT takes 11 hours or so directly from Flinders St station into Central Station in Sydney.
I stayed in mainly YHA hostels - though slightly more expensive (by a couple of bucks) they were far cleaner and nicer places to stay. If you want to party party party then the independent hostels are ok, but most of them we stayed in were dirty and noisy, and the clientel were mainly 18 year olds who were drinking themselves from Sydney to Cairns.
I lived and travelled in Australia for a year and still have tonnes to see, but you'll have a great time and meet some great people whatever you choose to do!
Just make sure you don't stick with backpackers, and try and meet some locals as they will show and recommend the best places to visit and stay!
Have a great time
