Don't bother with the brown sugar. Just use corn sugar. It won't do anything drastically different.
I've never boiled a vanilla bean with the sugar, but I'm imagining you're going to get an intense flavor from that, and it might be off putting. I'd stay away from it. Also, with 1/4 pound of chocolate and 1/4 black patent, this beer is going to be dark. More like a porter than a brown, I'm thinking.