I would think that driving half way and then stopping over night would be best, so go from Melb to probably about Woolongong. That is driving up the inland route.That would be about 9-ish hrs driving. And then from Woolongong to Coffs is about 7-8hrs.
I'm not really sure on places to stop between Melb to Goulbourn, but Goubourn is a fairly decent sized town to stop at. Then maybe Hornsby before you get onto the freeway. Newcastle is about 2 1/2-3 hrs from there. Not sure between Newcastle and Port Macquarie, but Port is a lovely place. Then Coffs isn't too far from there.