Kauai is fantastic. I am sure you will love your time there.
I dove with three of the operators while there and have no complaints about any of them. Be sure to dive Sheraton Caverns. During my dive on the caverns there must have been over 20 large Hawaiian Green turtles.
I would suggest you do a Na Pali coast tour while on Kauai. It was totally AWESOME and I am not easily awed. We did ours with Blue Dolphin and it was so fantastic we did it twice. They stop for a period of snorkeling and for a few extra bucks you can scuba instead.
We did three Luaus while there and each was very different from the others.
The first was on put on by the locals as a fund raiser for the building of a community kitchen just north of Hanapepe. It was in Nov but I am not sure if it will be while you are there or not but if it is it is a great glimpse of what an authentic Luau is like. I am sure if you ask around in Hanapepe you can find out when and where it is held.
I believe that Smith's Family Luau is the longest continuously running Luau on Kauai. It is held outdoors in a large amphitheater with tiered bench type seating. Very enjoyable and the food was ok too.
Lu'au Kalamakū was held inside and is a much, much, more theatrical production. Seating was more like banquet seating and it is held indoors. The food was a bit better than at Smith's and the experience over all is a little more upscale than Smith's.
We really enjoyed all three Luaus. Each was a very different experience and which is "best" would just depend on what your tastes are.
"South Pacific" was filmed on Kauai, and there is a dinner theater production of South Pacific at the Kauai Beach Resort. This is one of the things that is widely advertised and touted on Kauai. We went and were both very disappointed in it. The quality of the production was inferior to that of our local high school and the food was average at best. I would suggest you skip it and use the money for your Na Pali coast tour.
We are still deciding whether to return to Kauai this year of hit some place in the Caribbean or Central Amerca, but if we do Kauai we will be there in November as well.