I'm having trouble understanding how the barracks work and what some things mean.

First I have two on my crew that have a little gray icon above their heads that you can see from anywhere you are on the map. What does that mean and why is it important that I know where they are? I checked which members they are and one is a "standard" allies raider and the other is a players Jorms I recruited.

It says I can recruit 100. Why would I do that? What's the point unless it plays in later on. Should I save my silver for now?

How do the barracks work with switching people around? It shows 6 warriors when you configure barracks. Are those 6 the ones you are putting on the boat with you for raids? Does it make a difference who you take?

Thanks for any help.