The problem with cohesion is that the whole city is elevated (duh, ita a portuary city), so in order to combine all the sets, you would need a lot of pieces to elevate each middle size set, thus increasing the cost :'(
What nationality you ask, I would tend to go for the French Empire, but really it doesn't matter. That's one of the whole point of a portuary ccommercial city, you could have a diversity of nationalities mingling at taverns.
Sure they would not produce a slave auction :-D (OK sorry, very bad humour *wacko* )