One film, maybe!
I used to use two identical cameras (Nikon F's) with flash units, same film and alternate cameras to insure if one failed I still got results when I did weddings commercially.
Now that I use two Leica M7's, only one has a flash. One has K64 and one K200 of which I have small supply left. The K64 camera and flash are used with a 35mm Lux ASPH and the K200 gets a 21mm ASPH for shots from the back of the church and a 75mm or 90mm ASPH for shots at the alter.
With today's SLR's I would think that one camera with a good zoom and dedicated flash would suffice with one film. Possibly changing to a higher ASA for available light shots.
You must scout the church before hand preferably at the same time as the wedding to note light levels and access paths. I usually leave a bag with film etc in the loft area readily positioned. I always make contact with the server and define the rules for flash/no flash and access beforehand.
Find the rooms where the bride prepares and where the groom prepares.
Have a step by step plan from the arrival of the party to its departure noting when and where you will photograph. Good luck!-Dick