My usual strong preference for rooms that are meant to be lived in is to plan them to serve us in a variety of ways, and floating a couch in the middle of a normal-size room focused only on a TV, its back to...nothing, is so limited. Doesn't matter how many people have been doing this, there's more to family living than watching TV and a living room needs to accommodate other activities. Like chatting quietly with a friend, sitting together or on the phone. Organizing a club project. Building a dinosaur while dad keeps an eye on the TV. If it were mine, I'd sell the entertainment system and probably put a couch on that end wall, consider reconfiguring the sectional so the short piece backed to the wide top doorway, but the long stretch facing out into the room. Flat screen TV on the short wall in the lower left corner (happily hidden from entry too). Easy chair, or even two, in the middle (swiveling?). A secondary conversation area (chairs or chair and loveseat) by the fireplace. Or a reading corner and in the other perhaps a small card/games/project table or a desk and chair (facing out into the room). All open and sociable. The idea for a backless sofa is also an extremely nice one, but with the combination of a normal-size room and all those doorways/fireplace I would personally definitely pass on two full sofas with backs and otherwise keep the arrangements nicely open to each other for active living. (No neck strain from trying to admire the dinosaur without getting up.)

Will you actually use the fireplace? How much use will the t.v. get? Is it for occasional viewing or nightly viewing?How much use will the t.v. get? Is it for occasional viewing or nightly viewing? Which direction are those windows facing? This arrangement is not good if you will actually use the fireplace, with one of the couches with it's back to the fire and neither near it. If you go with this t.v./fireplace arrangement I'd consider placing your sofas in an L so both can view both the t.v. and the fireplace. With windows on three sides this seems like a problematic room for t.v. viewing, as I'd assume you'll get a lot of glare. Perhaps you could put the t.v. opposite the fireplace, and arrange the furniture so that there are two seating areas? Also, make sure you're mocking it up with furniture to scale so you can see what will work.

Although mounting the TV over the fireplace is not the most ideal location, in some instances it is the only option. The room layout has a lot to do with the placement of the TV screen - open concept construction, multiple windows, etc. We do many TV installations over the fireplace, mostly at the insistence of the designer and/or home owner. It's not the worst location and there are many trade-offs with this type of install. 55" and 65" TVs, for us, have become the most common sizes for installations in this situation. If you move forward with your installation, try and keep the TV as low as possible - I would suggest seating somewhere between 8 ft to 13 ft back for the TV sizes mentioned above.

When the sofa faces the window, the chaise completely blocks the fireplace and looks like a fire hazard. Since you're open to some construction, you may want to consider removing the mantle, adding brick up to the ceiling, then mounting the TV lower than where the mantle is now so it's more comfortable to watch when the sofa is facing the fireplace. If you remove the radiator in the dining table area, will you also be able to remove the 27" and 24" wide wall bump outs on each side? If you can, you'll gain valuable space and may be able to use the table and chairs you have now.