@teleport:
There's no script, but you can use a bunch of invisible teleports that point to the same teledest. (although confusing for the user)
Or you can let them into a room that uses a trigger to lock the door and force them into the only thing in the room, the teleport.

@enemy:
I'm pretty sure, but I don't know how.

srbs

If I am correct, you can make certain monsters in it by numbers. (though I have had some trouble with it a long while back.) The best idea is to spawn each one of the monsters you want to add in the map and then by clicking on their ent box you can type /mymapmonhellpig = [newent monster 1 2] and keep finding thier numbers for the map till of course you got it.

Note: I was using the numbers 1 and 2 as examples for the model and monster type.

Both require modifications to the source.
Modding guide, and see the links at the bottom of that page. (Though these mostly refer to total-conversion mods.)