You have a good size room and should be able to do whatever you want to, be it a 5.1.4 setup, a 7.1.2 setup, or ideally, a 7.1.4 setup. 10 foot ceilings should be really good for atmos, as you will have no problems getting separation from the base layer and the top layer. I would do a bit of research on the atmos configuration before making the placement final. I believe the rule of thumb is 45 degrees in both directions, which would be determined quickly by taking the distance from your ears to the ceiling (which I am guesstimating is around 7 feet), then going that far forward and back of the MLP to determine proper placement. If you can't get it exact, that's ok, just as close as you are able. And yes, I would recommend getting atmos speakers that you can angle in toward the MLP, or at least tweeters that can be angled. The blue speaker positions for side surrounds look fine, but I don't think I would make the rear surrounds in-wall at the current position. You may want to do on-wall, bookshelf speakers on stands or floor standing speakers for the rear surrounds, which would let you angle them in toward the MLP better, or place closer together if desired. As for speaker selection for atmos, you have a lot of good choices and I think you are on the right path. If you want to match with your 703's, you may want to consider the Polk Blackstone TL3's.