First, I own an Olympus C-5060 (older than SP-350, but similar in capabilities), an Ikelite housing, an Ikelite DS-125 strobe, and an Ikelite DS-50 strobe. I've also owned the Olympus housing for my camera.
For the SP-350 housing, the Olympus housing is $190 and the Ikelite housing is $440 (at B&H). I'm not sure that I would spend the $440 on a housing for a mediocre $200 camera that is probably near the end of its production cycle. I have a problem spending more than two times the camera cost on the housing which will lock you into that aging camera for several years.
I suggest that you plan your purchases with upgrading in mind. I would buy the SP-350 ($200), the Oly housing ($190), and a used Ikelite DS-50 strobe with a manual controler/sensor (as low as $200) or perhaps a used Inon strobe. This way you can continue to use the strobe when you upgrade the camera or sell it later for almost as much as you bought it. Now you've only spent $600 and you can use your strobe with future equipment, either as a fill light, a backup light, or your primary.
I used my DS-125 strobe with the Oly housing and a slave sensor for a year before I broke my Oly housing and upgrade to an ikelite with the insurance money and more of my own. The slave sensor technique is quite servicable. The DX-750 strobe also functions as a slave. Yes, the Ikelite TTL is better, but how long do you want to stick with the SP-350?
Just my $.02
David