If it's to scale, I would personally prefer a wider spread between mains. I'd also look into spreading the surrounds further out. I am not guaranteeing that these things will be superior, but I am led to believe they probably would be for me, and so I would immediately try those things out. Oh yeah, if you do spread them further out, please experiment with healthy amounts of toe-in. Go all the way where the left speaker is firing at your right ear, and vice versa. You don't have to keep it like that, but I'd love to know what you think, assuming you spread them further out to begin with. Remember to try to finagle a bit of extra space away from boundaries here and there if possible.
For the sub, put IT at your LP. Then start crawling around. Mark a few places where it sounds best, and then pick the one that doesn't get in your way or looks too wacky of a location. Then, what MDS said.
