Dummy battery and a USB-C PD bank gaffer taped to the tripod leg. Check the bank actually puts out enough watts for the dummy, a cheap phone bank sometimes doesn't and the camera just shuts off at minute 20.
Big card, and drop to a lower bitrate codec, you don't need your best 10-bit ALL-I for a locked wide. A long-GOP 4K file at a sane bitrate is plenty for a backup angle, and an hour of it fits on a card you can afford. Flip the screen out if your camera runs warmer with it closed, and keep it out of direct sun through the church windows.
And bring a second card even for the locked-off. If one fails mid ceremony you want to be able to swap it in thirty seconds during a reading, not hunt for one in the bag.
File splits line up fine in Resolve with no gap, at least on my Lumix. Can't speak for Canon, test it at home with a 45 minute recording of your living room before the first wedding, not on the day.