Tell your wife congratulations - sounds like fun!
The coldest I had my K7 was -38C for an hour. Even with high wind chill, single battery was fine. I gave up well before the camera did.
Your gear list looks good - I wouldn't bother with a WR lens.. the biggest issue with cold is the transition back indoors. I would recommend taking some large zip-top bags (large enough to fit the camera with lens attached.) Just before you come back inside, put the camera in the bag and seal it. Once you're inside, let the camera warm up inside the bag and you won't have to worry about condensation.