Having gone through this a few years back, I'll give my two cents - for what it's worth.
I got there early - to get a seat on the aisle, and to get close (but not too close) to the front. Since the rest of the pew was empty, when other started to file in, instead of sccoting down I stood up to let them get by me. Once they saw the camera, I think all understood what I was doing. While I'm sure every church/priest is different, there didn't appear to be any "restrictions" on people with cameras. There were plenty - many with flashes.
Our church has the typical 457 foot ceilings
so I've found the flash is really only good for very close range. Since it sounds like you will probably have pretty good natural light, I'm sure you'll be Ok. I chose my position as I wanted to be in the "right" spot to get them coming down the aisle - in BOTH directions - (hence the not too close comment above), and still be close enough to the front to be able to zoom in on action at the alter. This strategy seemed to work pretty well. I did notice some of the parents taking the opposite approach. They got in the pew, and slid all the way to the outside. Then as the ceremony was progressing some of them would get up and stand next to the massive pillars that are at the ends of some of the aisles to get shots. The pillars help to shield them from some of the congregation, so they didn't seem too intrusive on the ceremony.
For the most part this event is attended by some regular mass-goers, but mostly it seems it's the relatives of the kids that make up a lot of the audience. I would think the general expectation is that there will be LOTS of proud/happy relatives that wish to have picture taking be part of the event.
Good luck.....
Tim