I believe that there is carter post, only it is being located in a village and you can't build any new one.
I agree with the thing with limitation of buildings, but there is a way to change that building limit. Unfortunately I think this enabling more buildings can cause some lag - now and then the game freezes, and one second later it goes on (it doesn't crash)... At least that's how it acted to me, but I don't have some hell of PC though.
Regarding those inns... I believe that you don't have to build several inns - you are able to make your people more ale from the top right panel, where you give your people more food, set taxes, and stuff like that.
I hope it is possible to make a neutral village in scenario, so a player could take it over by sending his troops there... Still I'm not entirely so sure about that... Right now I am still winning the military campaign after I won the economic campaign, and I play some custom scenarios now and then. I'm sure I don't know all aspects of this game yet.
Also, it is not that I want to defend Stronghold 3, it's only that I believe that Stronghold 3 does have those features you mentioned, but if it really doesn't have one of them, then yes - it is something that should be in this game! There are even some more stuff that would be great in Stronghold 3.