Some thoughts:
1. The castle system is too early
The Castle system should not be available until the Iron Age. Let's look at how you get castle points:
Successful battles & negotiations - Bronze Age(limited) - Iron Age(unlimited)
Finishing big Guild Expedition encounters - Iron Age
Buying items from the Antiques Dealer - Early Middle Ages
Winning biddings in the Antiques Dealer - Early Middle Ages
Successfully finishing daily challenges - Iron Age
→ Finish them in a row for the special daily challenge reward - Iron Age
As we can see, most of the possibilities of scoring castle points we get in later eras ... In addition, the rewards we get from them will not be known by a beginner player, so introducing this system from the tutorial is pointless.
2. Expansion of the tavern
Here is a good opportunity to introduce the 4th column in the tavern shop which will be associated with the castle system. We players have a lot of Tavern Silver and we have no way to spend them ... that's why I propose another buff that would require a large amount of silver to spend.
Example: