Hi Serambin - I have used the same setup for some 2 years and without strobe (3 weeks ago, I got YS-110, see below). You can get pretty good pictures as is, but shoot in full manual mode. Start with shutter speed of 1/125th and aperture of 5.6. Leave the shutter speed fixed and change the aperture according to conditions (should be fine in the clear waters of Roatan). Ideal distance to subject about 24-30" and leave in macro. Although in exceptional clarity, I've had images up to 50'. Adjust white balance to red by about 4 clicks. Also, get photoshop (usually just fine tuning brightness/contrast).
Now to strobe as mentioned above - not a very satisfactory experience. The YS-110 has two manual settings 1 & 2, plus DS-TTL (slave mode, on), and TTL (slave Mode, off and used with TTL cable). Manual 1 is for pre-flash cameras. In synchronisation test, manual 1 seems to be the setting for the Oly 5000. Except, it only flashes once when setup. To get it to flash again, you have to turn off, wait a while then turn on again. The strobe flashes everytime in manual 2, but no pictures (synchronisation??). I am presently shooting in DS-TTL with slave mode on and with fiber optic cable. An arrangement not mentioned in strobe manual. However, in this mode, the 12 manual output settings are disabled. Camera preflash malfunctioning?? Or, some incompatibility with strobe?? Macro shots are going to be burnt out (will have to peel off mask and shoot on internal). Not a happy camper. Having said this, I've already had a couple shots in murky waters, that would not have been possible with the internal strobe.
Hopefully, I am better positioned for an upgrade (whenever).