You have plenty of time in 15 days see the places you list and include those suggested by others.
Personally, I would not use AirBnB. On the rare occasions I tried to use them on my last trip ( North Coast NSW to Melbourne and back via South Australia and the east coast) I was only able to book one - and they cancelled on me.
However, if you try it and they cancel, on your route there are motels in every town. As well as wotif and hotelscombined look at the Goldenchain site for possibilities, but in quiet June (school holidays don't start until the 28th) you will find many motels post signs out the front for last-minute discounts in the afternoon.
I've listed places to investigate in addition to those you mentioned. I suggest you search on these regions and towns for more info. Many are seaside or estuary towns, but also consider seeing some of the ordinary little towns along the way, such as Taree, Kempsey, Wauchope, Macksville etc, dropping into a pub or RSL/Golf club for lunch and a chat with the locals.
I like to vary my route away from the highway occasionally. Between the Hunter Valley and Forster or Taree consider the back roads via Dungog and Stroud. Try the side trip to Bellingen up the beautifuyl Bellinger River valley. I go from Coffs Harbour to Graftoin via Glenreagh, and continue to the Tweed Coast or Byron Bay evia casino and Lismore.
Bon voyage :)