New to MTW2 - where are my borders?

[FactionHeir]

v on a place hats too uneven/near forest to build a watchtower

Not true in M2TW. You can build anywhere which is not adjacent to another unit/agent that is not of your faction, inside your own region, not affected by any announced/unannounced disaster, next to another fort/watchtower.

You may think of point v when point iv occured, as you wouldn't know if iv occured or not until you realize you can't build anywhere within that region.

[Ibn-Khaldun]

.... next to another fort/watchtower....

So .. I can build forts next to forts too??
I have tried this but seems like I cannot do it