Macro shooting once you start approaching 1:1 is really best thought of as a specialized form of stop-action photography. The slightest movement is going to be amplified and very obvious when you're filling the frame with such a small part of the subject. The gear should be more than adequate for what you're doing.
As such, external light is especially important. If you're shooting TTL, the easiest way to approach this sort of shooting is to
A) shoot manual and use a fast shutter speed that will give you the exposure you want and also minimize any camera shake or subject movement
B ) be sure you're choosing a aperture that will give you the depth of field that you're looking for
C) get your lights as close to your subject as feasible - this reduces the flash time which is effectively a "virtual shutter"
Usually you'll be using manual focus, which is that much harder to use underwater when your entire body might be moving by even the most minute current - but tip C really helps reduce this a lot.
When I started to approach my macro shooting with this train of thought, a lot really started to come together for me.
Good luck!