I have a friend who did much of her travelling by finding other travelers a few years back ( with a vehicle ) mainly by checking out notices in hostels so you ought to do that and post your own in Melbourne, Adelaide ( if going through ), Perth, Broome, Darwin etc. as you go.
There's also a backpackers facebook forum, mainly re looking for jobs but also a few posts on there re travel and some people may look to move to somewhere else to seek work - https://www.facebook.com/groups/backpackerjobsaustralia/
It'll already be starting to warm up as you head north up the coast so make sure the vehicle cooling system is in good nick and have a few spares like extra spare wheel, fan belt, radiator hoses etc. as well as carrying plenty of water and a couple of jerry cans of fuel.
Good luck and have a good trip.