Hi Oldtoby,
Regarding Combat Advantages: They are rolled at the beginning of each close
combat encounter, not each combat round. So if your players ran into a party of orcs in the morning and were not taken by surprise, they would get to roll for Combat Advantage once at the beginning of the close
combat encounter. This is done after the initial volley if there is an opportunity to do so. If later that evening the party stumbled across a cave troll cooking a tasty dwarf with mushrooms and carrots, then the players would get to roll for another Combat Advantage at the beginning of that close
combat encounter.
Regarding Stances: You are correct, the heros just declare what stance they intend to fight in. I found this confusing too as stance is not related to position. I figure that a character can be fighting defensively whilst standing at the front of the fight, sacrificing opportunities to strike in favour of blocking and parrying attacks.
I could be wrong though, I'm new too
Cheers,
Kurt