Gold Coast to Melbourne - Which way ????

Do the Newell Highway, plenty of good free camps along the way, Mendooran, Forbes, Jerilderie, Tocumwal.

Have a look at the best motor museum in Aus at Forbes.

I can't help you with Victoria but I travel inland NSW regularly. I absolutely loathe the Newell Highway, it's just plain ugly!
But if you were after the quickest way from Gold Coast to Melb., you have to pick the Newell if you are towing, as do all the B Doubles!
Slightly depends on what time of the year, and middle of winter is not the best time to be inland, so I suppose you may be looking at a lot of coastal routes.
To me the most picturesque area of inland NSW is what is called the slopes, but it tends to be undulating, a PIA if towing.
If you are heading through Tamworth, consider going across the Liverpool Plains (genuinely amongst the best farming country in Australia, up there with Darling Downs, Atherton Tablelands, Central Highland in CQ, Yorke Peninsula and parts of the Wimmera), through Coolah, down to Gulgong (town on old $10 note), across to Wellington, Molong, Cudal, Canowindra, Cowra, Grenfell, Temora (then you can go across to Newell @ West Wyalong and south or through Wagga and Albury and south). But again remember the average overnight temp is likely to be zero (or lower).

There are numerous places to camp on the side of the road, or the small town council CP won't cost you much.

Again depends how much time you have, but if you head down the coast past Coffs Harbour, you are pretty committed to going through Newcastle and Sydney. I can't help you much with the NSW south coast.