The Fuji F50fd is fully compatible with Inon's accessories. As long as you keep the ISO under 400, resulution will be spectacular.
I have a Fuji F31fd that I use as a backup. I prefer the F31 because it has a much bigger battery.
What the Fuji cameras do not have is full manual control. It will give you aperture or shutter priority. I generally select aperture priority. Then I use exposure compensation (+ or -). This is with either my Olympus or Fuji.
The other major difference is that the F31 and F50 have very basic flash settings. My Olympus SP-310 and Larry's SP-350 have two flash options. The first is a slave setting in which the camera only emits one flash (no preflash). You can control the output on a scale of 1-10. This is used to trigger a bigger strobe. The advantage is that it uses less battery power. The second is using the regular flash mode (with preflash) and the ability to have flash exposure control plus or minus two stops. The Fuji F50 probably doesn't do this either. If you get an Inon or Ikelite strobe, this isn't a problem, since those strobes allow you to add some manual compensation. You may want to ask Larry if his new YS-110 does that.
These are links to my two recent galleries.
First is taken with an Olympus SP-310, Sea & Sea wide angle lens, Heinrichs Weikamp DA2 adapter and a Sea & Sea YS-60 strobe. I kept the YS-60 on 1/2 or full power (no TTL was needed). When you click on the photos, you can see the exposure information. It will usually show aperture priority, -2/3 or something like that. I did use the slave flash setting, so it doesn't show flash used.
Diving In Eilat/Red Sea Photo Gallery by Josh Krancer at pbase.com
The second gallery was my F31fd with a Magic Filter (no flash). I did not have a wide angle lens fitted to this camera, so the perspective alone is different.
fuji_f31_underwater Photo Gallery by Josh Krancer at pbase.com
You may wish to also look at the Canon A570is. They are inexpensive and have full manual control.
Lenses: I would start with the Inon AD-105 wide angle.