I have this camera, too
I use the Canon housing and it works just find. The white balance on this unit works well, so learn how to set your MWB if you aren't going to buy a strobe. The internal flash works just fine as long you are in range. I find that I have to turn the flash power down one notch or it overwhelms my subject. If I want to shoot stuff that isn't quite so close up (ie not at minimum distances, but not too far away), I simply bump the flash output up a notch - remember to turn it back down
There are quite a few choices for strobes. My personal experience and opinion is to spend a bit more on a strobe now so it will move with you when/if you change systems and you don't have to go through it again!
The Ike 50/51s are nice little units that will be a great start for you - but they may be a tad limited if you move systems and want to shoot wider stuff. They'll still work, you won't have to throw them away, but some people find they don't have quite enough for those situations. I've seen compact digitals with Ike's big gun, the 125, and it works very well. It will also move to any system you care to move to in future. Be warned, this is not the cheapest alternative and it's a big sucka!
I now use the Inons (after using Ike's, which I still have but don't use as much). They are smaller, lighter and provide excellent coverage. Buy the one that also takes a hard wired synch cord, not just a fibre optic cable and you can take the Inon with you wherever your uw photo takes you.
A good thing to keep in mind is
photography is light. Expect to pay more for your strobe than for your compact camera - light it everything and it isn't the place to skimp!