So it seems to me we have two options on how the placard works.  Passive, which would mean that everyone in the bar is safe as long as Mac is alive.  The protection is a 'threshold' sort of protection.  Or non-passive which would mean that Mac himself has pledged to fight for and protect anyone seeking sanctuary in the bar.  Either way Mac is putting himself on the line and as is said, taking a side.

Well, first, it's "Battle Ground" 

1-Yes, I agree with you. I don't think she knows all what is in Harry's head, but I think she has access of some of it. I don't know the details. That said, the explicit verbal communication between Harry and the queens was, I believe, a magic effect generated for the battle and not something that is always "on".

2-You are not the first in suggesting that Mab is grooming Lara as WL. In this same forum we argue that in several threads. I agree, only because that provides a way out for Molly. And because having Lara became a virgin, unable to have sex, would be very ironic. But besides that, I think that Mab wants to use the mundane connections and resources of the White Court. Lastly, she now knows that Lara needs to keep Harry alive, and she is providing a good way to her to be near him. And an engagement with the White Court would provide Harry with a good protection now that he is not White Council anymore.

3-Not proven, but I agree Mab knows Marcone (please, his name is Marcone) has Namshiel, and she is planning her revenge.

But did Mab know about Marcone before the ending meeting in BG?  Seems like when Harry called him Sir she had an epiphany and I thought it was that she figured it out right then.

Exactly, but putting his blood on the Placard and hanging it up, is.

You also have to wonder if there is a cost of some sort that you eventually have to pay to gain the protection given by the Placard.  Maybe something like his life force is tied to that location now.

If there's a law of magic for it, there's probably going to be a book where harry breaks it (or bends it into unrecognizable).
There's a WOJ out there somewhere that says something along the lines that Harry's going to break them all eventually.  Sue was my favorite crime so far!

I remember hearing that too, that before the end Harry will have broken every law of magic.  Which means at some point he will time travel.

I took it to mean that the bar has super protection, everyone in it will be safe, as long as Mac is alive.  Which puts a huge target on his back.  I didn't really take it to mean Mac himself will be forced to become super fighter to protect others.  But he will be put in a position to fight to save his own life, if someone wants someone else in the bar dead.

Was it said somewhere that most mortal women don't survive the birthing, or that it's hard for them?  I mean, the demon doesn't kick in until the Wamp kids hit puberty, right?  I'd imagine it's not trying to feed until they're older.  But I can't recall if something was said about that.

That is the impression given from the descriptions of 'coming of age' white vampires, from the youngest Raith (Inara or something?) and from the short story with River Shoulders son.

I'd be kind of disappointed if Harry starts leaning on Lara's political connections.

  I doubt he will, but that doesn't mean Lara or Mab won't step in anyways.  For a hypothetical example, Harry gets accused of Murphy's murder by Rudy.  He's at the station being questioned.  Now leaning on that connection would mean he would call on them to come help him.  I SERIOUSLY doubt Harry would do that.  What would happen is the questioning would be interrupted by a high dollar lawyer (sent by Lara or Mab) and that lawyer takes care of the situation.  Afterwards Harry might even act a bit miffed about it.  Or just decide "Hey, I am the winter knight/Lara fiancee, that might as well be good for something".  But calling on them when in trouble will never be his go-to play.