Excited to see the progress. Id seriously consider not doing that open window to the other room, if I were you. I would keep it a dedicated theater room with sound insulated walls and ceiling so that sound doesnt go all through the house. We did this on my parents basement theater room in their old house, helped quiet things down.
Id also put the projected wall to be the shorter backyard wall, that way you can do stadium seating in that room with 2 couches one in front of the other. But if you keep your existing set up, it will be nice either way.
Also your downstairs is open to the lower level if i remember correctly, so the sound will travel upstairs easily.
Otherwise plan on keeping the volume down low on that serious speaker system, so the baby can sleep.
