Rug size depends on the kind of furniture you use. I prefer short legged sofas sit with their front 1/3 on the rug. Leggy chairs look better entirely on it, and swivels need it under so they don't wobble when turning. If you have a very large room, you can use a rug that will allow for all the seating to anchor entirely on it like an island for conversation and TV watching. Minimum would be 2 feet wider than the sofa and long enough for the chairs to also be on it. Keep it 12-18" away from the hearth. Painter's tape on the floor is your helper, and you'll be able to see how close your furniture arrangement brings you to a standard size rug that gets the right look for your room.

I like you leather, it works with the stone fireplace; possibly stain the mantle a dark color to coordinate with the leather and the curtains. You could possibly add a pair of lounge chairs, one in corner by TV and one opposite it on the corner of the sofa....this will allow more seating and also allow the Hubs chair to stay in place for TV viewing. Here are three rooms that might inspire you.....the room below has some interesting elements to accentuate the height; it also has a nice furniture arrangement; if you could find another leather chair to match the one you have then add a fun color chair in the corner it would look pretty stylin'....and there are a lot of accessories in this room you could apply to your room beside the art....painted ceiling, hanging chandelier, large entertainment center that helps to balance out the large wall. This is a great Pit area with a lot of seating and a simple design plan that really looks welcoming. Lots of colorful pillows and a mirror go a long way for style in this room Beautiful use of color to soften up the leather pieces in the room and simply done with curtains and again pillows and white paint for contrast and architectural style.....the small area rug really adds some punch to the room for a nominal price.....this would involve investing in a love seat that matches or coordinates with the leather....color match or contrast would work well.

I am trying ti figure out how you would watch TV witha sectional in the window space. Sectional are actually the worst possible seating for comfort since only 2 people get an arm and everyone is lined up like a kids botrhday party. I would leave the space in front of the windoes as clear as possible. As for heat get some solar shades on those windows now, they will help with heat and damaging UV rays and let you keep the view.The TV is mounted a bit high and the black cabinet really doesn’t work with the rest of the pieces.

If you want to keep the sofas in same spot I would set the TV up in front of the Bay window and find a TV stand with storage for some of your children's toys/projects. That or place the Tv on the stair wall and set up the couches around that. I think the key is finding something that can store your childrens stuff so you can open up the room.