Sorry to drag up an old thread, I am sure you have made the trip to Belongil by now. For anyone else that might want the perspective of a newbie nudist, I went there recently, it is easily accessible by driving down grays lane, you can stop part way down the unsealed road to take a dip in the Tea Tree Lake, This is a great spot if you are timid, the water mostly obscures your body beneath the surface and being surrounded by nice bushland means you can find a nice secluded spot to try stripping off without feeling like you are out in the open.
About 2km further down the road is Belongil Beach. I am not sure where the authorised nudist bit finishes, but we just stripped off and made ourselves comfortable near the dunes just after the path from the carpark. There were a few other nudists but it was a weekday, so not too busy.
It is a beautiful part of the word, and even nicer that you can enjoy it nude, I left feeling well and truly refreshed.