As FBC's architect will tell it to you, the entire building will never be occupied by more than 344 people on both floors. Ever. I take issue with that. Namely because it's based on a non-existent section of the code. If you can find any section, clause, article, etc...of our building code (Yorktown uses the New York State Uniform Building Code) that defines and outlines parameters for "non-simultaneous occupancy," then
I will buy you, +1, dinner at Le Bernadin. Leave your citation, with contact information, in the comment section below.
[click on image; image get bigger]2nd Floor:
1st FloorPlease note, this floor is never to be occupied while the 2nd floor sanctuary is. That's right, the nursery and classrooms will never be occupied while there is a sermon upstairs. At least that is the narrative being put forth by the design team. I'd like them to cite the section of the code that allows them to claim the entire first floor as "non-simultaneous occupancy."

This shows you that the code is absolutely silent on "non-simultaneous" occupancy. It's an undefined term and not allowed under any circumstance. Perhaps the Town Supervisor or Building Department Commissioner can grant a variance for such?
IBC article explaining why they don't like, or define, "non-simultaneous occupancy"