The Queenslanders might think winter is good for travelling
but the further south you go the colder it gets.
Are there places/attractions that you really want to see or are you just planning on seeing how far you can go and what ever is on the way is on the way ?
Some I guess must see places would be Blue Mountains (west of Sydney)
maybe head up to Dubbo Zoo then head south again down the middle of NSW
Cross the Murray river into Victoria, check out Echuca (historic river port)
Make your way through Victoria via Bendigo & Ballarat (Soveriegn Hill is a very popular attraction),
Keep going SW to Warrnambool and then either head towards Melbourne via the Great Ocean Rd,
or Head towards Adelaide via Mt Gambier and the famous Blue Lakes then back to Melbourne
Once in Melbourne you can either take the short less interesting route to Sydney or go via the coast
Either way you go there is plenty to see if you check out ahead what's on the way, many interesting towns get bypassed by the freeways, so good to know what's in them before you go flying past.
As mentioned, Camps Australia Wide is the best source of Free / Low cost camp areas
October would only be busy if School Holidays are on (usually end sep - start oct)
Too many places to mention, it all depends on what kind of things you would like to see, eg. nature or man made.
Some national parks have long waiting lists for camping reservations.
When you have to wait a year to sleep next to a tree, something is wrong. ~George Carlin