My idea is to replace the current secure zone with this.
From the road entrance, have the public zone ‘branch out’ until it reaches either:
A fence, a vehicle checkpoint, a security checkpoint or a secure zone exit.
I would also do this: replace the current premade security checkpoint with a custom built one. Passengers will all do this: have their ID/boarding pass checked (by default by a member of staff, can then be upgraded to biometric scanner then an even an e-gate at some point), place their baggage on a table (can then be upgraded to a scanner), then they will be checked (either by a compulsory pat down, metal detector + pat down, or metal detector and full body scanner) then before finally going to pick up their bags from the table/scanner (possibly have another chance of a check there).
I would recommend making this a room, like baggage claim and requiring a separate staff-passenger security check.
I would have staff man different areas, decided by the CEO themselves.
Now, why would you bother upgrading?
Basically, if you have high passenger volumes and low security, you have a higher chance of attack (which cancels the days flights and costs money). Basically the airport will have a Security Level (obtainable through procurement). A CEO can impose more security checks (less liquid allowances, take off your shoes).
I would then have an appointable Chief of Security who can help unlock security upgrades and will impose (or just recommend) higher security checks.
Also, queues overhaul. Most airports have large queues for multiple items. So, draw a queue from the menu and then connect that queue to (an) item(s). For example, in a check in area, connect the end of a queue to all the desks.