[MENTION=6700238]Seven[/MENTION], about the rank for your slayer fighter. The whole world of Eberron has just emerged from a century long continent-wide war, so you could easily be a returning soldier of pretty good rank (captain to colonel, which would have given you command of between a hundred and a thousand or so men). You don't have that rank anymore, but your past military service could give you nominal command of the current operation to retrieve the Raven from No Man's Land.
I call it "nominal" command because, when we play, everyone gets to decide what their characters do and nobody will get to order anyone else's character around. With that said, you could be the person who receives orders and information from superior officers in the Watch and passes them down, and who talks first when your group is interacting with other people in an official capacity.
If you have another idea for your rank, I'm happy to hear that, too.