G'day Liventhedream. Welcome. I don't know much about the NSW leg of your trip. From QLD up a lot depends on what you want to see and do, and how long you have to do it. If you want to follow the coast just come up it and turn left at Townsville. Last time I did it that way there were a lot of road works. If you wish to come up inland QLD there is plenty of sight seeing to be done. Once you reach Mt Isa there is really only one way. Across the Barkly Highway to the Stuart Highway and turn right. I personally do not travel between dusk and dawn. Lots of cattle and other animals on mainly unfenced roads. Fuel should not be a problem but you will pay for it. There is only one place to fuel from Cammoweal  and the 3 ways. It is the Barkly roadhouse and he charges a fee for opening after hours. If possible I would suggest carrying 20 ltrs with me for emergencies. (others will disagree with this but I like to be carefull) I would also seriously suggest you get a paper map Of Australia so you can see the distances in the outback. What ever you decide travel safely and rest often. Mobile phone coverage is almost non-existent out side of towns. The wet season (for what it was) is almost over so should have no problems with floods. There should be plenty of others on this forum who will offer advice on this.

Cheers Jack

Hello Liventhedream

Firstly welcome to the forum, and I hope that you have an enjoyable time, in the playground

There are many roads to choose from, and I am sure that more seasoned travellers will come along, and probably give a much more scenic and/or shorter way
Unfortunately I was not on a time restraint when I travelled from Sydney to Darwin, and I followed the advice of other travellers on the road, of interesting places to see

I went from the Sydney area, to Katherine (300 kilometres or so south of Darwin) then turned west to my home base
I was in a petrol vehicle towing a caravan
I had no problems obtaining petrol along the way

If you get the Camp 8 book, and/or the Wikicamps Australia, for a laptop, they both show all the camps, both free and paid ones.

I left Richmond a northern suburb of Sydney.
Headed towards Newcastle on the Princess Highway
Turned off towards Tamworth on the New England Highway
Stayed on the New England Highway until Toowoomba
Turned off onto the Warrego Highway until Dalby
Turned off onto the Bunya highway until it intersected with the Burnett Highway around Goormie
Stayed on the Burnett Highway until Biloela
Turned off onto the Dawson Highway until Springsure
Turned off onto the Gregory Highway until Emerald
Turned off onto the Capricorn Highway until Longreach
Turned off onto the Landsborough Highway until Cloncurry / Mount Isa (not sure where highway started/ended, as I was using GPS)
Turned off at Mount Isa onto Barkly Highway until Three Ways
Turned off onto Stuart Highway, which goes through to Darwin

The only longest stretch was Camooweal to Three Ways, which was about 520 kilometres, so unless your rig can safely do this distance, you can purchase fuel at Barkly Homestead which is about 326 kilometres after Camooweal, and about 217 kilometres before Three Ways. I suggest that you purchase a bit of petrol at Barkly Homestead, just to keep this place alive.