Feudal System: I think monument is a piece of crap. What about this:
There is provinces from the begginning of the start and there is borders between them. But theese provinces are named Neutral provinces.

İf a guild builds a keep in a province, that guild become county and guild leader becomes Count.

When you built a keep, you gain both control of all county(on paper only) and a castle domain. A non-clan member must buy cells from the guild to do anything in the domain claim. To upgrade the Castle Domain, you need to level up the keep
(Saxon Hall->Wooden Keep->Small Keep->Medium Keep->Large Keep). You need to terraform for the next level of keep to upgrade keep. When you press Upgrade Keep a structural framework appears around of keep. When you gather enough resources and manage to finish the keep, next version replaces old version and your castle domain extends further.

Military Buildings can only build in Castle domain but Unique Economic building can only build in villages

If there is a keep in the county, you cant build another.

A non-clan member can do everything in the county (outside of the domain of course) and can build a Saxon Hall. If a player builds a Saxon Hall in a county, a village domain area appears. Same thing as keep but you cant control a county with Village Hall. Villages cant build stone fortifications.

Villages can grown into Towns, then Cities. Upgrading extends the Village Domain area. Upgrading is same as upgrading county. Firs Village Hall, then Town Hall last City Hall.

Monasteries can be build outside of all domains. They can be upgrade to Holy Order Headquarters and can build religious and some unique military buildings. Monasteries have no military buildings nor economic buildings. They are only for religious buildings.

Counties can vassalise other counties. If a county vassalage another county, liege will become Duke. If a Duke vassalise another Duke, liege will become King. If a king vassalise another king, king will become Emperor.

Counties can implement their own currencies or adopt other currencies. They can determinate the weight of the coins. Heavier coins have more value.

Coin weight can be in theese standarts:
Full (Gold: 1000 Silver:100 Copper:10)
Half(Gold:500 Silver: 50 Copper 5)
Quarter (Gold:250 Silver:25 Copper:2,5)(If you are using Quarter currency, you cant demand or offer anything with odd copper. You must use even amount of copper because any other currency cant give you decimal value.)
Tithe (Gold:100 Silver:10 Copper:1)

Coins will have "Value" stat. Lets say Gold coins from B county have a currency that have Full standart coins and A county have currency with Tithe standart coins. A merchant goes B to A. He saw a carpet on the marketplace. Seller demands 10 value for it. If merchant had 1 A silver, he could buy it but instead of the A silver, he has 1 B copper. Now he can buy the carpet with only 1 B copper.

If a county swears fealty to another guild, that county will use currency of their liege and leave their former currency. You must remint the older coins otherwise they cannot be use in trade.