I shoot a D70 in a Sea & Sea housing. I like the housing a lot--sturdy, reliable--and will probably stick with S&S when I upgrade my camera. FWIW, friends who have other housings seem to have more leaks and other complaints. That said, no housing is waterproof if not cared for, so whatever you get you should plan on being REALLY diligent about cleaning o-rings, etc. All it takes is one stray hair for your expensive housing to become an aquarium, and your expensive camera to become a museum piece.
Sync cables seem to be the weakest link in the chain. They are prone to stresses and strobes have pins that are too easily bent. A tiny amount of water on the contacts means an electrical short and therefore a non-working strobe underwater--I know from experience--so make sure you keep everything nice and dry. I suggest a housing with a separate port for each sync cable. Mine only has one port, requiring a Y-cable to use both strobes. The Y-cable is not made anymore, so if mine goes out it will be hard to find. (I think I can use a TTL converter, but I haven't had the need to try that yet.)
Being a pro on land, you may find yourself frustrated underwater at the lack of control over everything, from lighting to subjects to keeping the camera still. A couple of photographer friends have often gotten out of the water and jumped up and ready to quit.
I echo what others have said about lenses: you'll shoot either macro or wide.
Can't wait to hear what your experiences are like and hopefully see some of your pics. Welcome to a new world!