Kauai is a great place to see.......much more rural and true to original Hawaii than any other island. If you get time, spend some time on Oahu to see the touristy stuff (Pearl Harbor, Arizona memorial, Bishop museum, Polynesian Cultural Center, etc)- then you'll appreciate Kauai all the more.
I think most of the GNs are on Oahu, but it's been 13 years since I moved back to the mainland......