Weather that time of year is ideal. From Kailua south is usually mild, even cool at times, esp from Kealekekua on south. In 8 or so trips in early Dec, I've encountered bad weather only once - last year's 50 year storm that silted the ocean for several days - and regularly good seas. North of the airport is windy, or else windy. Also far from almost everything, and expensive. I hear good things about Jack's but have always rented with Big Island Divers because their gear rental prices were better. I dive a lot when there and the very different tank policies made a difference, don't recall for sure about the other gear I take all my own now. I've only done Manta dives with BID, and liked their operation. Staff and owner Norm are nice folks and helpful. Condos, even on the coast where you can shore dive in front, can be had for ~$110 or less per night. Traffic along the highway above Kailua, in either direction, can be heavy around commute hours but is easy to time.
OK, now I want to go.