Aloha from Kauai!
Just wanted to offer my help with any Kauai diving info that you may need. I am currently a DM/instructor here on the island and have been for a little over 12 years. I think you'll find a number of dive companies that are very professional here and more than happy to help you out. If you have specific questions at any point feel free to send me a "PM" and I can respond quickly.
The basics...
Summer diving on Kauai is great and offers lots of variety. The majority of the diving is on the south side of the island. Two full service shops(boat,shore,store etc..) run out of Poipu and one "boat only" out of Port Allen. There are about a half dozen smaller shore diving only operations. The shore diving will be done at two locations during the summer months 1)Tunnels Beach on the north shore and 2) Koloa Landing in Poipu (south). Tunnels is a topography dive primarily and though not much marine life is to be found - it is a very impressive lava tube tour. It also boasts one of the most beautiful backdrops for a shore dive you'll probably ever see. Koloa Landing is very critter intensive and a great spot for turtles, moray eels, lionfish, octopus and occasional frogfish and harlequin shrimp.
You are pretty much in the middle if you are staying on the east side and will find that you drive north or south every day more often than not. It is a small island though and you'll find drive times are not all that bad. As a side note if you would like to get any information on other activities, places to dine etc. just let me know. I'd be happy to help you out in any way possible.
I personally work for SeaSport Divers in Poipu but have worked with all three of the primary dive shops on the island. I maintain close relationships with both the owners of Fathom Five and Bubbles Below respectively so I can set you up with contact information for them as well.
As is the case with so many things - I think you'll find that it isn't finding the Business/Shop to go with, but rather the Instructor. Kauai has many GREAT instructors/DM's that have many years of experience. Regardless of who you choose to dive with always remember that you can request specific instructors you have heard about (or minimally request an experienced/patient etc. guide).
Well, great news to hear that you have a new dive buddy in the family! Always makes it more enjoyable. Sheraton Caverns is a must see dive here in Poipu for our amazing and abundant Hawaiian Green Sea Turtles!
Feel free to contact me as questions come up.
Have a great weekend and weeks ahead as you count down the days to Hawaii!
Anthony