Here is what I was taught, and seemed to work for me:
wrt white balance, you shouldn't set it if you use a flash, or should set it to auto in that case. Things came out a bit odd when I manually wb'd before flash. In natural light, wb is key if you are below 15-20 feet.
You can fix wb in raw mode, and can even adjust it with photoshop on jpeg- just not without loss.
There are lots of disagreements on whether to use TTL for your flash, and whether a ttl cord is worth it. For me, I went with the new Canon G9 as the replacement for my Casio 1050 in order to get RAW, ttl, better glass and Aperature/Full manual modes.
From what I've been told, especially if you are switching from close up work to further away work (hey look, shark!), TTL just makes it easier. Yes it is harder to bracket your flash output with TTL- even if you push the EV up or down, how are you sure it is metering the same spot? But for a newcomer to flash UW photography, I think I'll be using TTL for most shots.
If your camera doesn't natively support RAW mode, you might look to see if it is one of the Canons that has been hacked to support it-
http://scratchpad.wikia.com/wiki/CHDK/FAQ