I watched the video tutorials by Smeer Kat before embarking on this project, his recommendation was to add 16 PlayerStarts per team, so I took this very literally!
But thinking about it again, with a certain amount of detachment, spreading them out across a wider area might have reduced opportunities for spawn killing. Perhaps placing one near each side tunnel entrance, and others closer to the base of the ramp, for example.
The flag area doors never fully close. They're both on a random timer that fires about every two or three minutes. I wanted to create some sense of a story, as though this arena is in a state of degenerative decay, perhaps as the result of past conflict (though scorch marks and other damage might have sold this more convincingly). So the doors are malfunctioning and the projection of the team logos is subject to intermittent flicker.
If you look at the inner door at the far end of the flag area, you'll see (at one end) symbolism from the Fallout franchise. And if you listen closely near to that door, you'll hear the sounds of an Enclave officer muttering to himself on the other side. If you fire below the door, he'll react, and shine a light in your direction. It's even possible to "kill" him with a carefully directed shot (actually, I've only tested this out with secondary fire from a rocket launcher, but it might be achievable with the shock rifle from a wide enough angle).
On the equivalent door of the opposite base you'll find a poster from City 17, the main staging area in Half Life 2. And behind that door (faintly illuminated by the flares), if you're able to detect it over other game sounds, you'll hear a Combine soldier engaged in radio chatter. Again, shooting under the door will alert him to your presence and modify his dialogue until he gives up on looking for you. You can take him out too, if you're lucky. Though you have to pretend that both he and the Enclave officer are immediately replaced by another soldier.
I'd originally planned to script this so that they'd wander around behind the door, and you'd be able to follow their progress by watching the path of a beam of light. But when the geometry side of things dragged on, I lost enthusiasm for spending more time on the scripted elements.