Yeah I think you're right about the agents. I think it's one per chain, regardless of level so to speak.

Might be worth it to build one of the top level markets to get +2 xp Metsuke though? If you bother to get that far with the Chi, that is.

Though I consider Metsuke to be the least useful agent to be honest. I rarely bribe, Monks can boost happiness in a region (right?) and ninjas can "apprehend" ;)