Great work on the Kingdom!
A few comments:
- Not all nobles of a same rank are equal in actual power. Baron 1 might be an idiot, baron 2 might be a friend of the king, baron 3 might rule over nearly worthless land and be broke, baron 4 might have a crack team of problem solvers (the PCs...), baron 5 might have elite troops etc etc.
- The actual power of a noble is in part based on the power of his vassals and their relationship to him/her. So Duke 1 might be in theory the most powerful noble of the land, but his counts hate him and constantly plot to undermine him. Meanwhile Duchess 2 has far less territory and income but her counts are loyal and competent.
- I was going to comment on the Marquis but someone already did that. In theory the Marquis will be skillful commanders and have good military troops. In theory.
- Make sure that each "rank" has their own land on top of the land of the vassals. The king has several private estates, but so do the dukes (to a lesser extents). The counts usually has the "best" barony (more income, bigger size etc) when compared to the barons.
- Usually, A noble can only go one step directly below him/her for help. If the queen summons the forces, she asks the dukes, who then ask the counts, who ask the barons; she can't ask the counts directly, (appart from the counts who report directly to her)... in theory. In practice if a duke gets asked for help by the king, does nothing, but the counts underneath him are loyal to the king they might go over his head and help.