Hi Adam:
I would direct you to read the reply by James to my post below this one. This would be a good starting point for your camera as well. BTW, I have the Canon S-500 which uses the same underwater case as your's. My housing leaked on my first dive! Not from the rear seal but from the zoom button on the top. Apparently, this was enough to stop my camera from operating and I could not use it for the remainder of my vacation. I did purchase an underwater strobe from Reefmaster for the camera which worked out very well. I also bought a wide angle lens from Inon for the camera which is made to fit that particular housing. Interestingly, there was another diver that was using your exact set up with no strobe or WAL and was getting excellent underwater photos, especially after I discussed some of the settings suggested by James with him! As long as you are in water with excellent visibility and have sufficient sunlight penetration, you should be able to get excellent quality photos underwater. However, under more demanding situations, a strobe and wide angle lens would definately be a plus.
As a side note: I called Canon about the warranty and they said that the housing is NOT warranteed at all and that if the camera had water damage that it would not be covered either. Well, I went nuts on them and wound up writing a letter and sending the camera and housing to their service department anyway. They had better cover these products or I will report them to the better business bureau and elsewhere. So, bottom line, beware if anything happens to that housing while diving. Good luck and good diving.
Steve