There is a WoJ on this that I believe was something along Thomas wasn't planned and he was the result of all the awesome vampire sex.

I recall this WoJ too.  Wasn't planned, was very unexpected -- whampire-babies don't often carry to term.

From what others have written on this site, Butcher has said that the demons that make the White Court vampires and the White Court mantles don't mix, which lead some to conclude that Dresden and Lara are unlikely to consummate their arranged relationship.  But in the released chapters of Twelve Months, Mab is pushing hard for Harry to sleep with Lara ASAP.

And given the apparent ground rule from those chapters that Lara can't use her Whampire powers on Dresden - and she's suppressing her demon for the dates - that consummation would occur while the demon is basically unaware/asleep/unconscious/whatever.

What Mab's play here?  Does Dresden or Winter gain some level of control over Lara or her demon if that consummation occurs while the demon is incapacitated?  Or is Mab counting on Lara conceiving a child with Harry?  There must be some advantage that accrues to Dresden or Winter for Mab to be that interested in Harry and Lara sleeping together at the earliest possible moment. 

I think Lara is simply being very-careful to keep her Hunger "satiated" when she meets with Harry.  It isn't "incapacitated," just much, much easier for Lara to keep under control.

I'm unclear why Mab is pushing for this; as you say, we've got WoJ that the WK-mantle issues around sex/violence and the sexy Whamp-mantle play together in uncontrollable ways.

I suspect Mab's agenda is either:
- to put extra pressure on Harry to find another solution
- to get Lara killed, by way of triggering Harry's Mantle
I suspect she has contingency plans for either alternative.

I don't feel I understand Mab's "big picture" in this, however!

How does Mouse talk though?  Telepathically very likely as in the person he is talking to hears his words in their mind and believes they hear him talking.  Dogs cannot talk like humans because their muzzels just are not built for human speech, that includes Mouse. 

I suspect Mouse speaks Doggo; and very eloquently!
It's heavy to body language & facial expressions, with some limited vocalizations.

I expect most dogs understand Mouse almost as well as Harry does, tho likely when Mouse tries to "discuss" more complex issues, the average pupper will get very confused... "Dafuq he sayin' ??!?"
 

They know what materials they should use, but using them depends on the short term.  Short term as in what is the cheapest and the quickest to get.  Usually very little thought is given to the cheapest and quickest now costing more later and taking more time because it will have to be done all over again at a later date.  Sadly politics do enter into it as well, that gets very complicated and ugly. 

There's also the well-intentioned "we'll put up the building NOW, with the materials we can get NOW, because otherwise folks will be unsheltered this winter."

Limited availability of "preferred" materials -- and limited budgets -- are all-too-real things that can force unwelcome choices.

... Harry knows and understands what kind of dog Mouse is, they communicate very well, Mouse doesn't have to speak human language to make himself understood. 

Well, Harry knows now.
He surely didn't always know!

Though I think he still has some wistfully envious moments when he notices others who can actually *talk* with Mouse in casual conversation that Harry can't (yet) quite match ...

... Second Q:  Will they consummate?  I think yes, too.

I don't think they can.
Some time ago, WoJ stated that the WK-Mantle combined with Whamp-Mojo in really bad ways: the only possible outcomes would be a mentally-broken & fully whamp-enslaved WK, or a dead Whampire.

Harry will go to the bathroom right before heading to the altar and ... transfer to Mirror Mirror land, leaving Lara at the altar and Mab seething. 

This is my theory, more or less.

Maybe not a bathroom, maybe just the changing-area where Harry takes off his jeans/T/duster uniform & puts on a tux (but it still has the necessary mirror for checking fit&c...)

I don't know, I can see it go either way, the thing is I don't think Lara wants to get married anymore than Harry, between the two of them, they may be able to outsmart Mab.

Agreed:  neither of them really want to marry.  The thing is, I don't think Mab wants that, either!  I think she has a big ol' pile of other agendas based on her telling them to get married... including forcing them to work together to (try to) outsmart her.  Mab being Mab, I'm sure she has contingency plans for if they do get married, but I think her preferred option is for them not to.

The main questions I have are:  is it a full swap, with Mirror!Harry coming to Harry!Prime's world (where he's expected to go through with the marriage to Lara)?  Because that's part of the OG Mirror,Mirror ST:TOS episode, with evil!Kirk&co coming to the Federation, and Jim has been frank that he's stealing shamelessly there.  And then (also based on the ST episode):  is it just the Harrys who swap, or is it Harry plus a big pack of his Scooby Gang (and if so, who?) swapping with Mirror!Harry and his Posse?

I can just imagine the moment when Harry is standing there at the altar -- seeing Mab(??!?) in the front row of the audience -- and waiting to see who his bride is... aaaand it's Lara Raith, making Mirror!Harry go "o shit, I thought I was going to a safer universe!"

Meanwhile, Mab is thinking, "what the fuck have you done, Dresden, where is Winter's Knightmantle??!?"  And when the officiant gets to "Speak now, or forever hold your peace," it's Mab who speaks up.