Why wouldn't you put them both centered on the wall? You don't say what size fireplace you are getting but once you get the firebox installed and stone/tile around it you will probably close to 7 feet for any reasonably sized fireplace. If I did the fireplace on the side with very little tile around it, I would use the other side for a tall shelf and still center the TV above the FP. Personally I don't think putting a TV above a heat source is a good idea, but that probably depends on how much you use the fireplace. If you have the fireplace picked out or any drawings of what you are thinking about, post them here so more people can help you. The more details you can offer the better feedback you will get.

Those are great, CeleryGirl. I guess I am going to think about adding the wider window on the right only. The one that's there doesn't open and it's too close to the fireplace. Do you all think the window on the right should be the same height as the front window? Should I ignore the ceiling slope or should I incorporate some detail over the fireplace that goes straight up to the ceiling?

Thank you MSDG I don't know if I'm doing paneling work -- I need help designing the entire wall. The firebox cannot be moved because there is an egress window right next to it on the outside (basement). I'm not looking for the black/white look, I was showing the photo for the mantle style. What do you mean "Furred out portion around fire box?" Do you mean the marble before the wood post section? I can't decide if I should do a heart or not. I like it sometimes, but I need to figure out the entire wall to see what looks good together. I also like the look of a window seat, but I don't want it to look so casual like a kitchen bench. Do you think I should put a new window only on the right side of the fireplace? What are your thoughts on a bench seat underneath it? Thanks so much for your help!!

@Patricia Colwell @Beverly @Mark Bischak @Debbie and Ed Butler all great suggestions and comments. Agree should have gone with a linear fireplace. But it's too late. The builder explained why the bottom trim is there now and the portion we don't want will be removed. It had to do with painting, but regardless it will be removed. There is something about a wood stained floating mantel that I like. But I could opt for a painted traditional style mantel with supports/legs if that look would be better for my space. Our ceilings are 16' at the peak and the room is large, vaulted and a lot of light. The TV will be a decent height for viewing. The room is really large. 36' wide by 25', though will have the seating area focused around the fireplace. The kitchen and eating area are on the opposite wall of the fire place (behind me as I took the picture. Open concept. And I do agree I should have chosen base cabinets and then done floating shelves instead of the big shelving units. But that will be a project for several years from now when I really dislike the shelves. But I do have a lot of fun blown glass and neat pieces to display. Back to the fireplace. Here is a pic of one I like 0 screenshot it off Instagram so it's not a full pic and I don't have a hearth). A question I have is how far across does the mantel go? and should there be a gap between the tile and the wall edge and mantel or is it ok to have the wall below the mantel completely tiled?