First, searching on "oly 5050" gets quite a few responses, and if you take the time to sort through, there's a lot of good information. Including:
1. Oly 5050 ISO settings
2. Oly 5050 My Mode
3. Oly 5050 flash settings
4. Super Macro settings
I think the point that people were trying to make was "help yourself, there's plenty here". You happen to have one of the most popular P&S digital cameras for use UW, so there's a lot of info out there.
Anyway, here's a couple of quick answers since your search was so fruitless... 
1. Shoot on Manual or Aperture Priority (assuming the 5050 has both). You want to minimize your aperture, so set it at the higher end of the range, f/8, f/11, etc. Set an appropriate shutter speed to stop motion, i.e. 1/60 or faster.
2. No, you don't "need" a red filter, but if you're not going to use your external flash, this may help you get more color in your pictures. Take a look for a thread on natural light or manual whitebalance to maximize your results.
3. Some people find using the internal flash or no flash at all works fine. Most people eventually start using a flash. Reason is, red goes away for all intents and purposes below 30ft.
Hope this helps. 
Tom
P.S. Ooops, seems Eric and I were typing similar things at the same time...