I don't have too much to add to what these other folks have already told you about the Bailey Range Traverse. I have done that trek a bunch of times in different variations since '69 (including a solo ski traverse in the spring of '92.) The usual camping spots on the full regular traverse (Soleduck to Elwha Basin, etc) might be Cat Basin, "Eleven Bull Basin," Cream Lake, upper Queets Basin, Elwha Basin, and anywhere down the Elwha valley trail. I guess it all depends on how fast the party hikes and what the weather is like. I second the advice on knowing your map-and-compass stuff well, in case you find yourself in the clouds. There are also fun peaks to scramble up along the way if there's time.
Hopefully, you'll get a chance to see some Olympic elk while backpacking through that high country. The high points of some of my trips in the Olympics have been seeing elk, occasionally in big herds and with some large bulls. Those bulls could be called the monarchs of the Olympics and if you're in the right place at the right time in the high country in late summer/early fall, you'll hear them "bugling" in the course of the mating season. Ages ago (mainly in the '40s,) a fellow named Herb Crisler and his wife Lois used to hike the Bailey Range, making films of the elk and other wildlife in the mountain splendor. A good book about their adventures is "Beyond the Trails: with Herb and Lois Crisler in Olympic National Park" by Francis E. Caldwell.