Awesome idea!
I think it would be cool if in addition to that if/when villages are added it would be nice to have a village elder NPC that you could go and ask if anyone wanted to follow you. It wouldn't be guaranteed that there would be someone looking for adventure but you could hire various NPCs such as lumberjack, soldier, cook, miner, etc. They would cost varying amounts of rusty gears depending on skill level and equipment. They would follow you to your settlement and you could tell them which house to stay in.
I also think that depending on certain things could be added to buildings to give them a purpose for certain NPCs. For example a long building with a bunch of beds and a fenced in area with dummies in the back would be a barrack. Soldiers staying in the barrack would recover faster or gain skills quicker if that was implemented. That way it would encourage players to have various buildings in their villages instead of one block building that is repeated.
I like the tax idea but what if there was a tax collector NPC that you could authorized to collect taxes for you. That way if your kingdom gets huge then you're not spending all your time running around at the end of the season collecting taxes. You could give your tax collector a edict telling them what percentage to collect. Now if we wanted to get really in depth then if you taxed your villagers to much then they might revolt. There could be a lord NPC that could help keep the peace in your absence and he might be able to command soldiers to stop the riots.
An added factor in multiplayer could be the hiring of spies and they could go to different villages and try to convince them to secede and join their kingdom. Their success would depend on the influence of the local lord. If he was weak then there would be a high chance your village would secede to the enemy side.
