I shoot RAW, and would advise you do - it will give you the best chance for recovering shadows, highlights and fixing colour balance.
Aperture priority and auto-iso will probably work well, but don't forget to set a minimum shutter speed, I typically use 1/250th to avoid motion blur. If you leave it on 1/f or 1/60th you may get lots of blurred shots indoors.
Since I often shoot wide open (f1.4), I will jump to shutter priority - it will force wide open, and I get full control over shutter speed to either freeze action or lower ISO for stationary subjects.
I go full manual when working with flash later in the evening, usually for cake cut, first dance, and disco shots. Perhaps use TTL and bounce flash off light ceilings or walls for better lighting. You may want to practice indoor bounce flash, depending on how familiar you are with it.
I don't know what kind of lenses you have, but consider stopping down to get important shots, such as a shot of the bride walking down the aisle, the kiss, the first dance, e.t.c. it will give you more room for error, particularly if they are moving.
(stopping down for me is using 2.0 instead of 1.4, but your mileage may vary). Practice taking photos of someone walking towards you indoors.
Stop down aperture for group shots, particularly if they are staggered.