As for your capacity issues, I don't have too much in the way of problems. I shoot with a 1GB card and a 256MB xD card. That gives me something like 170 RAW shots or so. With a 2GB card and a 512MB xD card, you could have a LOT of picture-taking ability.
With respect to your question about 5050 and RAW, everything I shoot underwater since January or so of 2004 is RAW. The picture I posted was in RAW, and I believe everything on the website except for the Bahamas 2003 pictures were RAW and shot with the Oly 5050(above-water is shot with my Canon 20D). You are exactly right about my setup. It is an Oly 5050 with the Inon WAL and dome unit. I love it. Especially for shots like your first one on your web page. I like these shots where you get a person at the surface and can see the curvature of the lens. It's a nice effect.
I believe everything in my Bahamas 2004 collection was in full auto mode, no manual settings. I did no whitebalance beforehand. The beauty of RAW is that you can adjust whitebalance and other details afterwards. Another note, because I was shooting with the Inon lens, I turned off my flash. Make sure you do this. Reason being is that your lens will obstruct the flash and you will get a big shadow in the center of your picture. I had an INCREDIBLE dolphin shot ruined by forgetting this setting once.
I looked at your pictures and they are nice, especially for someone out on their first shoot! I am a bit confused, though. It looks like a spearfishing competition, not a freedive competition--or is it a freedive competition in which everyone must carry an object like a speargun?
A couple suggestions that may be of help. Being a freediver, I understand the need to not be distracted unduly, so you might do a couple things--switch to RAW, turn off flash, shoot closeup, do whitebalance afterwards. This might be difficult given light situations(Bahamas is a lot easier to get away with no flash than Sweden!).
If the water doesn't allow this type of shooting, I would definitely get an external strobe or two. And I would go with an Inon setup(if not two). I shoot with two Inon Z220 strobes to fully cover my Inon dome lens. I highly recommend Inon. I love Ikelite and will soon own Ikelite(DS-125 for my Canon setup), but as a freediver, I love the size of my Inons. 99% of my water experience is freediving and I can still handle the Oly 5050 with the dome lens and two Inon Z220s. When shooting with strobes in the Oly PT housing, you will need to shoot in manual mode. This takes a little getting used to. My bible for this is Peter Schultz's guide at Splashdown divers. It is EXCELLENT(Thanks Peter!).
http://www.splashdowndivers.com/photo_gall...up_settings.htm
If you look at my turtle pictures, a LOT of them are shot with dual strobes and I use a variety of settings. The ambient light fluctuates and so you need to adjust your settings depending on your light. In Hawaii near the surface, this is a pain in the butt because your ambient light can change dramatically in a split second. In green water, perhaps you can get away without making a lot of changes, hopefully. Either way, when you get there try to get out in the water a day or so before the competition with a buddy and shoot for a while to get the feel of it. Find some settings that work and lock them in with the MyMode feature. That will allow easy access. Also, if you are to use strobes, you might want to be careful about shooting directly in front of them on their descent. It would be very distracting. A side angle or even an up-down shot from behind might be better. On the rise, I would feel a bit freer to get close and do face-shots as they near the surface. Distraction isn't an issue so much and I think people really wouldn't mind getting their pictures taken "in action".
Just a couple thoughts, anyway. Hope it was of assistance.
--John