Sounds like an excellent plan!! If you don't want to drive early in the morning, your two choices for boat diving will be Extended Horizons to Lanai and West Maui or Lahaina Divers to Lanai, Molokini, and West Maui. If you don't mind getting up early and driving to Kihei, my favorites are Ed Robinsons, Dive & Sea, and Makena Coast Charters.
Since you're newer divers and coming from Kahana, I'd really recommend Dive & Sea for a couple of reasons: the captain is the owner and gives an extremely personalized experience taking only 6 divers on his very spacious and comfortable boat. Adam the DM is an excellent guide who sizes up his divers' needs quickly and does a great job taking care of them. They also go out a little later than the other operators (7:00am instead of 6:00 for B&B or 6:30 for Ed Robinsons), which gives you an extra 30 minutes in the morning.
For Lanai charters (and I recommend you do one) we prefer Lahaina Divers because of their spacious and comfortable boat for the sometimes rough crossing. They do take more divers, but their groups are broken down into 5-8 divers per guide, so you don't feel crowded.
Shore diving is very good, but I'd recommend hiring a guide if you aren't familiar with diving in Hawaii. There are so many endemic creatures and so many small creatures that are easy to miss, that the new to Hawaii diver will benefit by with a good guide to maximize what they're seeing.
if you don't mind driving to South Maui, I'll recommend shore diving with Sam from Maui Dive Shop, anyone from Maui Dreams, and Shaka Doug. There's also scooter diving....but I'm sure someone with first hand experience will pipe up and give you the scoop on that.