Wow, indeed. That is going to be a fabulous room, and those are the best diagrams I've ever seen. Great picture, too. Thank you for sharing your project with us.
My concern about the placement of the front speakers is early reflections from both the mantel and the base of the stage. It will probably be fine if not wonderful, but your plan seems to add a lot of hard surfaces very near the edges of the speakers, which could compromise the imaging somewhat. I don't think the height of the M60's are going to be a problem since you'll be a good distance away. You can probably make minor adjustments on the angle of the VP150 pretty easily if you need to by using a little wedge of some kind under the back edge.
If you're wiring at the moment, you might wish to hedge your bets on the subwoofer placement and wire a couple of different options. It might be difficult to get the placement nailed before you get everthing done and the subs acquired, and you might find that you like one of them in the back of the room or something.
I'm concerned about control of ambient light from all those windows.
Where does the equipment live?
Very exciting project. Congratulations and thank you again for sharing your journey with us.
