Ask the family about the details of the ceremony: location, time, how many people will attend, basic flow of events / activities. Based on this you can ask which moments shall be captured and where they might not feel comfortable if pictures are taken. Such a ceremony usually is not open for creative shots. Stick to what is asked for (and maybe paid for).
Low light photography without aid of flash. Camera with high ISO capability required. If Nikon - try D700 or better D3s; Canon - 5DII or better 1D4. At least now you got excuse to rent these camera to use, for serious photography you know.
Use a fast zoom like 24-70 f/2.8. f/2.8 aids in low night photography, zoom allow you to have the flexibility.