You could enter the country through Perth, Western Australia - the most isolated capital city in the world, but it is easier to get work. It's a beautiful city, great night life and gorgeous beaches on the Indian Ocean. There's the wine region of Margaret River, which is great for farm or fruit picking work and Western Australia is stunning, especially in the Kimberly region to the north. I highly recommend a visit, it's less populated than the East Coast and has amazing scenery. Exmouth, around half way up, is a great spot to dive and explore the Ningaloo Reef - it's less expensive diving here than on the Great Barrier Reef, and just as impressive. If you're lucky you can also see Whale Sharks around March/April. Further up in the north west, Broome is a lovely tourist town with lots of work during the high season (May-October) and you can even work on pearling boats out on the ocean for excellent rewards. I worked as a cleaner in a hotel - it was great fun and good pay. Broome also has a wonderful outdoor cinema. The town is well worth a visit. You can also get a flight to Bali from here as your nearer to Indonesia than most places in Australia.
Remember the seasons over the Tropic of Cancer, between October-April it's the wet season and it's not that easy to get around with a lot of flooding and road closures.
Travelling around is best done by car, perhaps getting together with other backpackers and buy a cheap car and camp - it's easy and cheap. But check out what you need with RAAC, it's easy to be ripped off and end up spending a lot on repairs in being stranded in hostile territory. The Greyhound Bus is another option, but you are limited on the West Coast. The only rail option is between Perth and Sydney on the Indian Pacific, an amazing journey or the Kahn from Adelaide to Alice Springs.