Hi J-Dog. Every diving environment is different. What I did before getting my strobe was play with the camera in the UW macro and UW wide scene modes. When I got good shots for my conditions, I looked at the EXIF and used it as a baseline for my manual settings. For macro work, 2 feet and closer, you can get pretty good shots with the built in flash (spot focus) as long as you have a closed background. If there's open water behind the subject, you'll get backscatter in my experience. In tropical settings, it's advisable to use natural light and manual WB for wide shots. If you're shooting a lot of pelagics and fast moving subjects, I'd turn off the auto focus and use manual focus for one of your My Modes. You can set the distance to your most common shot and it will default to that. Then you can scroll up or down with the mode scroll buttons to adjust. If you want fast shots, set up in the highest JPEG. I prefer RAW, because you can fix almost anything in a good RAW conversion program. Unfortunately, it takes between 7 and 12 seconds, depending on which card you have, to recycle for the next pic after a RAW shot. By then, the Turtle/Shark/Seal, etc. is long gone and you've got a lovely picture of where it used to be. I like to set up the four MyModes for four different type of shots, that way you can just push the mode button and scroll to the next one if you are changing subjects. Currently I have one set for SuperMacro in manual focus, one for Macro in auto spot focus, and two for wide, one with manual everything and one with autofocus and auto WB.
As far as strobes, get a good one to start with, because it's a lot cheaper than buying two or three before you get there. I ended up with the YS-110 and Heinrichs/Weikamp ttl converter. I spent almost as much on the two cheapies I bought first, and now I have little use for them.
