Aloha!
Sounds like you have a fantastic trip in the works! I agree that some of the south Maui sites are fantastic. Makena Landing is a fantastic shore dive that rivals many of the boat dives. While there are numerous great operators on Maui - I always use Mike Severn's Diving. Pauline, AJ, and the gang are awesome. In terms of critter knowledge and finding the best of the best - THEY ARE HARD TO BEAT! I love their passion for diving and the briefings on critters are out of this world. I've been diving here professionally for almost 20 years and strongly encourage divers to go diving with them. Even if you aren't staying near Kihei, the morning drive is well worth it. Captain Andy is also fantastic. A great captain and a great sense of humor. Super helpful as well.
Molokai diving can be fantastic. The only operator that goes (conditions allowing) I believe is Lahaina divers. Bigger boats with larger groups. I've enjoyed Extended Horizons when I've dove out of Lahaina.
Take a look at some of the posts about Niihau if you want to do the best of the best diving from Kauai. The local diving is spectacular as well and offers many of the same critters, topography, diving styles of the other islands. No wrecks to speak of, but great lava tubes.
While I personally work for Bubbles Below Scuba charters (under new passionate ownership, you'll find that all the operators here are very professional and helpful. If the waters have cleared on Kauai near shore - Koloa Landing is traditionally a fantastic critter dive that is loaded with turtles, scorpion fish, frogfish, and other exciting creatures.
Again, really look at Niihau! It's a full day of awesome diving with the rare chance to dive with the endangered Hawaiian Monk Seal!!!
Feel free to hit me up with any specific questions regarding Kauai if I can help you with any arrangements, ideas, or thoughts on land stuff etc..
Best of wishes as you plan for what it sure to be an awesome dive trip to Hawaii!
A