I got Kyoto and my god it earns 50k in tariffs!
Ahem anyways, got a few questions.
I got a town but I have a tiny oversight I forgot, how do I get vassals to join me when I haven't befriended any of them yet?
What level and skill should I get for companions to be vassals?
Mod specific questions:
Diplomacy mod allows you choose your faction culture, why do I have only Miyoshi and Usuegi clans?
I don't know how companions work in that particular mod, but if they were not changed, you should be able to send them to gather intel on a faction specific to each companion, and once they return, you will have a bunch of information on which vassals are resentful of their liege. If you meet them, you may use the 'talk in secret' option to try and convince them to join you.
If you ask around, you may also learn of the personality of a vassal, then you should use just basic logic to figure out what of the options in the argument fits their personality the most - a scheming cynic is unlikely to be moved by your goal of ensuring justice for all and none shall leave unsatisfied, or a martial lord is unlikely to desire to serve a ruler aiming to end the wars by uniting the lands under his rule.
As for Diplomacy, integrating the actual open source code into the mod is up to the modder, not the OSP author, so it's likely a bug.