To try to answer all three of these questions together:
I always thought of Office Complex as having two elevators- one on the East, and one on the West. In B Map, they correspond very nicely with the ‘antiroom’ areas in front of each staircase, but if we are imagining the floor as under a security lockdown in and of itself that presents a problem- there’s a double-door security checkpoint coming up to this floor from the one below it (or the elevator nearby), but not one from the other direction. Someone can come down from the cafeteria stairwell or take the far elevator and just walk right in. Therefore, I sort of thought that what we are looking at is a series of checkpoints designed to monitor and control the flow of personnel through Admin 1- you can get to any one section without necessarily passing through a checkpoint, but to go from the basement to the cafeteria you have to hit at least one. Therefore, since the south offices offer another path through the floor they have one and only one checkpoint.
The northern section, since by nature it has only one entrance, is my guess at a truly high-security section of offices- no elevator access allowed there, and to get in without Gordon’s all-access backstage pass you would need to be allowed into the security-office corridor by the guy in the open area with the couches, then let through the doors proper by the guard in the separate, currently closed-blinds office.