I disagree, No shooting in raw isn't a must, nor is a strobe, or even the internal flash. If you're relying on RAW to clean up grossly shot photos, then you should be getting exposures right during the shot, not pushing things on the PC
Sometimes depending on the shot, such as wide angle, and capturing a whole reef wall or school of fish, a strobe won't do doodly squat for you. MANUAL WHITE BALANCE, shooting off a white slate at depth works great to set what "white" is at depth.
Especially when your strobe dies on vacation.......sigh....yeah my DS-125 crapped out in Honduras....you have no resort but to shoot in manual white balance....and I'm glad it forced me to learn the technique.
In my opinion, the preset "underwater modes" settings suck, don't even bother with them.
The SP-350 joys are for it's manual controls, shutter speed/f-stop control as well as manual white balance. No it's not confusing.
Basic settings.
I normally shoot in macro mode, sometimes but rarely super macro, I love wide angle lenses, I'd buy an INON lens almost before a strobe, almost.......
ISO 100-200, 400 can get grainy.
Shoot the Highest F-stop you can, better colors and you'll not wash them out.
If possible don't shoot below 1/60th of a second.
Internal strobe is "okay" but is easily blocked by the housing, especially if you're using a wide angle lens. Yes a strobe of some sort is needed for shooting under a ledge or in shaddows.
Best advice, get Li-ion rechargable batteries (cheap off ebay) shoot shoot and shoot some more. I'll average 100+ shots per dive. I shoot exclusively in full manual mode, adjusting F-stop and shutter speed as needed for the conditions.
practice makes perfect.
here's some of my manual white balance work, from Roatan Honduras. I was playing with a INON 165 degree super wide angle fish eye lens.........drool....way cool compared to my 105 degree wide angle....165 is sweet........and no strobes were used, or could of been used, for all these wide horizon big reef pictures. I hadn't used Manual White Balance before, and now I'm a believer........
Learn all the features of the camera, 80% of good photos come from the user skills, not the camera itself.