I'm testing my design the problems I have faced so far:
1) Traders: using the raisebridge sealed entrance to the edge of the map, works quite well, I let them take a long path and my depot is in the middle of the map, I posted an animal watchtower above the path to detect any kobold/necro/ambusher that happens to spawn in those 4 tiles at the edge... Also traders without wagons (damned elves) when leaving not necessarily take the wagon road (the one with depot access) out, they just left through my kobold path because they don't set off citizen pressure plates...
2) I'm still testing my animal watchtower above the kobold trap, I pastured a pig on a grate above the kobold path and it reveals the kobold and runs away steeping on the pressure plate that would open the retractingbridge bellow the kobold path, the issue is keeping other roaming animals out, so I added a door pet impassable, still got to test if they run away to the pressure plate and back to the pasture on the grate if I designate it as a meting zone, and forbid the door completely to avoid dwarves going there...
3) Citizen pathfinding: my entry does its job sorting citizens from kobolds from goblins, but it depends on breaking pathfinding, creatures have 2 paths in front of them one closed by a door the other open by a floor hatch, they initially path through the hatch path, but just before they are able to get there there is a pressure plate that opens the hatch breaking that path and opens the door opening a new path, as said it works for roaming creatures but if the dwarves are hauling something (like logs from outside to the carpenter's inside or block from inside to the wall project outside) when the path breaks they drop the item on the plate and go on to another job... maybe I'll set up some sort of system with minecarts for hauling stuff outside-inside-outside...
4) Small creatures: domestic creatures smaller than an adult dog are too small to set up a citizen pressure plate, so they keep roaming on the goblin and kobold paths unchecked... solved by pasturing all the animals... also a 1-z-level drop like the ones produced by my opening hatches can hurt and even kill a small creature, I got a gosling killed that way...
5) Liason: not sure if it was just coincidence but I managed to set up a paved road on my wagon closed path and the liason spawned nearby, in contrast to when I didn't have a road that he spawned on the other side of the map...
6) Migrants... those damned idiots spawn anywhere, and by anywhere I mean they actually spawned on the side of the map where there is no access to my fort since the map is divided by a river, the river freezes but they spawned on the wrong side of the river in the middle of the summer... -_- I was thinking of making a special path with access to a meeting zone but they seem to completely ignore everything...??