Questions for game veterans (Assassin's Creed: Odyssey)

Good afternoon, while playing I have questions that need answers, help

Why, after the battle, is the leader absent and allegedly defeated? When will the new leader appear?

Does respawn exist in cleared fortresses without fighting for territory?

What does meditation affect besides the weather, the change of day and night?

For a long time I cannot understand what affects the fleet at sea, if the adjacent territories are under the authority of a certain side? (athens, sparta)