First, arrange the main seating area with the fireplace and TV as your focal point. If you like to see the TV from the kitchen put it on the left side of the fireplace. If you don't care about seeing it while in the kitchen, leave it where it is, but wall mount it on an articulated arm for flexibility, and put a new credenza below it that is 25% wider than the TV. We don't know where your dining area is, but you could put one at the kitchen end of this space. Or, you can use a family game table at the end opposite the seating arrangement. Replace the fireplace mirror with a nice big piece of art, but no wider than your firebox opening. If TV goes left of the FP you could move that slim piece that's by the pony wall opposite the FP, to the right side of it with the mirror above it as a balancing element. Or it can go on the full wall closer to the wide doorway. If buying new seating pieces, consider replacing the two wood trimmed chairs with something else. They seem to be misfits for the style of your other pieces. Rugs need rethinking, but get the arrangement organized first.