Another thing to consider for armed security - are there any safe lines of fire in your church? Our sanctuary is laid out like an inside sports arena with the alter low and surrounded on all sides by the people (no, it's not a big mega-church, just medium sized, but that's the layout). Even in areas where you'd normally expect a reasonably safe line of fire, you have to consider all the many people around in every direction. That "backstop" you see is probably just a thin sheetrock wall with a Sunday School class on the other side.

I am all in favor of being prepared and able to defend yourself in any location, including at a church, but a mature and responsible person will have thought about and considered safe lines of fire long before any incident happens. You should have already come to conclusions (just examples here) "I will not fire in the sanctuary due to surrounding people, but the doorway to the east parking lot is a possibility during dire circumstances." It sounds a bit dark to discuss things like this, but a reasonable security force WILL discuss things like this, in advance.