It's important to know if the couple will be facing the audience or the priest (Officiant). This will determine if you should place the camera at the back looking past the audience and to the couple OR from the stage so you can see the couple's faces with their backs to the crowd. You will miss the Priest's face but the ceremony isn't about him, its about the couple and their day.
 Also...you should be able to meet with the couple and ask what the basic flow of the ceremony will look like. What is their order or service? How long will it be (that will determine how many tapes you bring, etc). Get an idea from them on what the day will look like how to film it.
 Check out my site for more info and how to best shoot weddings. It's a resource on how to improve your video.
http://www.ImproveMyVideo.com
Jeff