Last thing you want is even the chance of blurriness if u can avoid it.

Since the pressure will be on, sharpness beats depth of field in every poker game in town when it comes to wedding photography. You'll be shooting at night - up the ISO to 1000 or more to salvage background detail. If there is no background detail to be had, lower the ISO to something less noisy as it's no use.

about that 1/50.... a bit too slow. The flash (I usually use TTL in all modes for events like these) should cover it but you may lose a few shots at that speed. I recommend shooting in manual mode if it is outside as the lighting will not change. Lock in the minimum shutter speed u need (easier to do in manual mode) and choose a wide aperture. Do a few on the spot tests. If you want to go semi automatic, to assure the sharpness, in this case because the pressure is on (first wedding) I'd recommend shutter priority at the minimum required speed (which depends on the lens of course).

Hope that may help - Good luck!