WELCOME ABOARD!
You are one of the few people who actually figured out the delay in the start of the war. Many people have logged in to ask why everybody hates them for sinking British ships, not realizing the war hasn't started yet.
No, there are no Rules Of Engagement in the game. Ships will not surrender. They won't stop. You can't board them. I sometimes make my own, only attacking from the surface when single merchants are involved, but the game isn't sophisticated enough to model any of that.