I think your line of thought is wrong (no offence)
You are thinking along the lines that gear will pull you through the day. (ie. lens and/or FF camera)
What you need to work on is skill and confidence in the equipment you are using (to adjust to the situation)
Practice shooting at home or some friends; practice how you use your flash; practice how you manage the crowd/guests to form up for the table shot.
At the least, talk/discuss about these things here, rather than gears, which is a small part of the whole equation (really).
My few cents :
1. I'll just take the 17-50 and a flash. Table shot, personally I find that even 24mm on aps-c is ok. Just need to form up the ppl in the table properly.
2. Practice your flash (preferably know how to bounce it); You can shoot your mother, sister, cat, etc, just practice and know how to control your flash bounce as well as ISO/aperture/shutter/flash pwr
3. Know your lens (not everything is shallow DOF; often times you need more DOF (eg. group shots) ). This relates to knowing your flash too. (ie. flash power; camera settings)
4, If you have a chance to attend someone elses wedding, try to observe how the photographer handles the situation