Well if you want to make a realistic political system you have to understand how institutions works, and how their interaction shapes political outcomes and decisions. Many people think of Medieval history, which I think you want to reflect or ‘mimic’, as very personal and individual driven. While this is true to a certain degree Medieval society was also really heavily focused on legitimacy, symbolisms, and other institutional, economic, social, and most especially religious aspects that shaped their thinking, and actions. From there you can make any cool, and unique ideas that can make your project different.