1- It's a history book because the boy tell his history with his father and the captain.

2- The boy and the captain will have more adventures in the sea's house, the captain was a famous pirate and he wants again arrive to the same place and tell his history as a pirate and the captain said the boy that in the box was a treasure and they have to search and lived happy for a rest of the life.

3- yes, only one

4- inn= public house, groundsel:
Ithink the inn is in the evening and everyone will attend