Make sure you let your officiant know you will have videographers present, as there may be rules for where the camera cannot be.
Most importantly, you will want to ask the officiant if we can plug into their PA system to record all audio from the venue microphones being used. Usually there is an audio technician that will need to be notified. Asking to plug into an audio system doesn't always mean you're going to get a "yes". Be prepared to force the issue, as you have invested in a wedding video and the ceremony is the most important part.
****This may seem unnecessary, or even a hassle, but it’s the best (and sometimes the only) way to get clear audio from all parts of the ceremony.