It's an easy drive though the first 200km has twisty bits. Can be done in 8 hours, 10 at most. Nothing really worthwhile for a stop en-route but Sale would have the most accomodation albeit not particularly charming. But there is an amazing variety of climate zones and thus vegetation and wildlife along this route ... much more variety than you would expect. Just don't expect man-made attractions like great hotels or zoos.
As for choosing between Eden, Merimbula and Bermagui, they are much the same (equally pleasant). Merimbula is significantly bigger than the other 2 (which are only a couple of thousand people, so all 3 are small towns). A beautiful part of the coast and quite unpopulated.