Generally speaking, the more you can see, the better.
(ETA: Yes, even though I outline this is pretty minimal cost etc, there's some permission involved, herding cats, scariness, etc so this may be impossible to even propose to the leadership at your place of worship.)
I am not sure I'd want to be in the main meeting room at all if I was the only armed response, or the leader. Be in a room (that no one knows about, with a locked door so no one can come mess with you... and never, never visitors) and cameras. Cameras anymore are cheap. Stream Wyze cams to a series of pawn shop tablets and you have a security camera system.
From here out, assuming what I picked up from the OP's stuff: The only armed person is in the building. I'd stay in my room. With a holstered handgun,
and a rifle in an opened discrete case (or locked up so it never leaves the room). You could even go so far as to take off your suit jacket, put on a PC an and extra mags. Have a large placard on the front and back that says SECURITY to help the police not shoot you when responding, to freak out the congregants a little less if you have to come out.
Audio and video to outside, entrances, and ALL off the main meeting room. No blind spots. Avoid pan/zoom cameras; you will get tunnel vision as you focus on one and drive it around. Need to scan the whole area and keep scanning until reacting.
Reaction is RARELY going to be getting out of your chair. Use radios. The ushers (I assume) stay at doors, respond to people wandering in late, etc, and are your first contact. You need to be in contact with them to get eyes on, to initiate contact, and to give you feedback. The goal is to never leave the room, to use your resources to avoid issues.
Have the phone number of all ushers. Make sure their phones are on vibrate, but so they will feel it and can answer. If f it's you, they know to perk up their ears, and pick it up immediately.
Oh, and and talk to local PD. See if they are happy with 911 if there's an issue, and if there's a way to shortcut the usual script in the event you have an AS/AK and need to just press a "panic button" as you have to react immediately. Make sure the ushers know to call also, and how. Laminated cards with this info are reasonable.
Do not fall for taking the White Settlement event as the way to go. The short engagement time is being touted I think too much as needing instant reaction. But think harder about it:
- No one usefully made contact with the shooter before he pulled the shotgun out. It is likely that he could have been kept to the side, maybe out of the room.
- That, among other things, means no one was close enough or of contact mindset to go hands on, to avoid him completing the draw, etc.
- The first guy to draw a gun was shot and killed. If that is the only armed good guy in the building, how does the rest of this event unfold? Badly.