interesting idea. Another thing I was thinking about is making several money sinks when dealing with housing. Was also thinking upgrades for housing. As land permits, your able to start with a shack, one room with a bed and a locker at best. As the size of the house grows, your able to upgrade things inside the house or buy new.
Several money sinks when dealing with housing are already planned. Rent on house or buy, upgrades to houses you own, more land to build up your house/estate. thinking shack - hut - small house - house - large house - small mansion(small estate, possibly multiple buildings, defensible), medium mansion(small estate or larger, definately more than one building, upgrades to defenses), large mansion(medium estate or larger, more than three or four buildings needed, Very defensible), small keep(estate, guard barracks, walls, defensible, aka first guild hall, starts city), medium keep(walls have towers), large keep(addition of moat to possible buildings, surrounds one outer wall, even it its inside the outermost wall), Small Castle(allows access to larger city buildings and various structures not available earlier), medium castle, Large castle, and then finally Kingdom Castle. Each would have a level of vault built in, some would have the ability to build a bank to allow your citizens to access a bank.