This is the beginning of a good plan. Security in depth. The 4 "D"s of physical security.We will have several zones with specific duties in each zone.
Detect. Early warning is your best defense. The easiest way is to have a lookout posted at a high window who can see them coming.
Deter. We have armed, uniformed, Sheriff's Deputies stationed outside our main entrance. Just seeing him there may deter those who intend harm and cause them to seek a softer target. Even non-uniformed security people will probably be noticed by an intruder and may cause him to go elsewhere.
Delay. This is where security in depth comes in. Have several layers of security to slow down the intruder. To get to our front door you have to climb about 25 steps. The outer doors are locked and are opened from the inside by "greeters" who are actually an additional line of defense. The doors from the foyer to the main auditorium are kept closed and latched (but not locked - fire codes). Then, just inside those doors are 6 ushers who are the next line of defense.
Defeat. I like the military concept of "Defeat in Detail." If the intruder is alone overcome him by weight of numbers. If there is more than one, divide and conquer. Take them down one at a time.
If it is necessary for the security team to discharge a firearm remember the "boarding house" rules of engagement. If there are three equally dangerous targets, "Nobody get's seconds until everybody has gotten firsts."