I hope you have a wonderful trip! I would totally agree with earlier posts that starting North is a good idea. Maybe after Sydney it would be worth flying to Uluru (Ayres Rock) or Alice Springs first... then QLD... then Tasmania. The Northern Territory and Northern Queensland will be starting to get hot by Sep/Oct - and feeling comfortable outdoors in these areas is so important as it is the outdoors where you want to be!
If you check out the AAT tours website (http://www.aatkings.com/au/) you will get a good idea for the kinds of itineraries that work around the Red Centre. You could then rent a car on the net or through a travel agent and do it yourself - or go with this AAT or another company to take advantage of the knowledge of the guides and pre-arranged accommodation etc. The distances really are huge - the chance to have a break while someone else drives could be really good in NT! Especially if you end up doing a fair bit of walking. You don't need to - there's still heaps to see - but getting further along tracks in the National Parks shows you amazing scenery. The fitter you are the more fun walking you will have. The Aboriginal Centre at Uluru and the local guides are great for information about Aboriginal culture of that area.
If this is the BIG TRIP (ie this chance may not come again) - it might be worth also looking at Darwin? Kakadu & Litchfield National Parks, plus the history of Darwin is interesting. In NT generally, check out history of exploration, the laying of the Telegraph, The Flying Doctor Service, School of the Air, plus aboriginal history and the current situation - it's really complicated. Many musuems and tours available. Lots of people to talk with.
I hate Cairns. Full of backpackers, horrible souvenir shops and pubs. BUT it is a great way to get to the Daintree and Mossman Gorge. It is also a good way to get to the Great Barrier Reef. But I would be inclined to see it as a base, or entry point to the area rather than a destination in itself. So get a car or book into tours. Tours to the reef and National Parks are plentiful and you could just sort it out when you get there - means you can adjust for the weather. You could also book 3 days at a resort style hotel in this area (Port Douglas?) and hang out eating seafood, drinking cocktails, lounging by a pool, having a holiday/retirement celebration!!
Southern Queensland, I would pretty much avoid south of Brisbane. The Gold Coast is really touristy and tacky. Maybe around the Sunshine Coast - Noosa or Frazer Island - would be worthwhile? But I actually wouldn���t make it a priority over Darwin for example. Brisbane is a nice city ��� but it���s just a city��� (Strong opinions I know - sorry Brisbane folk... it IS a nice place, but these folks only have 10 weeks!!!)
Ditto earlier poster's comments on Melbourne: Great Ocean Rd; Mornington Peninsular; McLaren Vale wine area all worth seeing. Plus Melbourne itself.
Self-drive in Tasmania is really really easy and fabulous. Food, wineries, scenery. Tourism Tasmania has sample itineraries and lots of ideas (www.discovertasmania.com.au/home/index.cfm…)
Once again - get into the National Parks!!
Apart from spending a few days being a tourist in Sydney, some easy day or overnight trips would be to the Blue Mountains (and out to Orange/Bathurst or even Dubbo and the Western Plains Zoo for the NSW country town experience); Southern Highlands (Bowral, Moss Vale via the M5 and back via Nowra and the Coast Road); Mudgee (farmland, wines, good B&Bs) or down to Jarvis Bay. Most people focus on the north coast of NSW - the inland is fabulous, but big, dry and the changes are pretty subtle. Up around the New England District is very pleasant for a driving holiday - you could spend 5 days on a real roadtrip from Sydney travelling up through Barrington Tops and the New England Highway to Armidale and Glen Innes, then cut through East to Grafton and back via the Pacific Highway. About 280km a day average. Many of the towns have museums and art galleries plus antique and second hand bookshops worth stopping for on the way. The "Land of the Beardies" Museum in Glen Innes is a great local museum - very personal to the area and also lots of background on Australian rural history. Run by volunteers and a wonderfully messy eclectic collection! (Look out for the amazing collection of barbed fencing wires from 1900 to the present for example!)
Don't know their schedule this far in advance - but one of the trips run by these companies could even be a fun way of seeing some of the country NSW!!!http://www.heritageexpress.com.au/saescape.htm
or http://www.3801limited.com.au/
My suggestion then would be something like
Sydney & NSW 14 days
Red Centre 8 days
Darwin 8 days
Cairns 7 days
Tasmania 10 days
Melbourne 7 days
You could pick up cheap one way fares on the websites mentioned in other posts - hire cars locally - add another 7 days to cover travel days between each area - and you've got a pretty busy trip with a few days of hanging out near a pool and relaxing as well!! Or add Adelaide and 2 or 3 wine districts if you are into wine. Or add Broome (WA) or Margaret River or Perth (also WA). So many possibilities! Across the Nallabor by train also springs to mind... Perth to Adelaide or the other way. (http://www.gsr.com.au/trainways/index.htm)
Generally out of the cities, cheap hotel or pub accommodation is easy to find via the local tourism centres, and you could play it a little bit by ear, certainly in NSW, Tasmania and Victoria country driving.
Sorry to rave on - but I love travelling - and Australia is great! Have fun researching and planning your trip. It's at least half the enjoyment. Wish I could come too!