1. A virtual centre is the way to go if you only care about the MLP. Otherwise, VP160HP. When you're watching alone, go virtual.
2. M2 will sound thin in that room. I'd go M5 all around and up top. I don't have experience with ceiling mounting so I can't make a recommendation. FMBs sound plausible.
3. Keep the room orientation as is so as not to block the windows.
4. As for the sides and rears, what a treat to have such tall ceilings! I would experiment with the sides and rears at various heights up the walls. If "too high" up, consider upside-down mounting so that tweeters are pointing to the floor.
