cruiser:
I've been reading your posts and looking at the awesome pics of the Flower Gardens and WANT TO GO.
How many dives are recommended before a trip like that?
I don't think you can measure it in number of dives, but if I had to put a number on it I'd say 40 to 50. Some may scoff and many novices have gone out there and had no problems. Many people also drive home drunk from the bars every weekend and have no problems. Getting away with it doesn't mean it is safe.
Some may be ready at 20 dives, some not even at 60. The real issue is that you need to be comfortable in the water (everyone says they are), familiar with your equipment, and have your basic scuba skills down pat. Task overload is the enemy. There will be enough unique aspects to ocean live-aboard diving that you don't want to be struggling with your gear or trying to remember basic skills. Your mind needs to be free so you can listen and remember the DM briefings and the specific procedures they want you to follow.
You'll need to be able to navigate back to the mooring line or stay within sight of it (which you can do and still have great diving). You'll need to be able to control your buoyancy as you will be nitrogen loaded and your safety stops are important. You'll need patience as there are lots of other divers all trying to do the same things at the same time. You'll need to be prepared as when it's your turn (to enter, to exit, to eat, to potty) there will be lots of divers behind you trying to exercise patience but expecting you to be ready. The crew will give you special help but they can't babysit you.
The diving is intense and everything operates on a tight schedule, almost military like. No single item is particularly difficult for even a novice, it's the cumulative effect that can be overwhelming. The more variables you can remove the simpler it will be. I'd recommend first taking a day trip to the oil rigs. If you can handle that you can handle FG.
P.S. I was on that rig trip with "pantysniffer" and can second the recommendation on Sport Divers.