The media cabinet is too large for your room and there are too many colors for your home that don't seem to correlate. No purple in the living area. I have lowered your TV and suggested a floating wall hung cabinet. Pull all your furnishings away from the wall a bit to the room can breath.

You have two nice features; the fireplace and the brick wall, plus a nice bit of light. Painting those dark blocks outside white will enhance the brightness and look cleaner overall. Then paint your walls that taupe/greige of the mortar on the brick wall. I think that color will work well with the fireplace too. Try two 3-seat sofas and two swivel chairs in a "U" in the middle of the room. The swivel chairs will close the bottom of the "U" and can turn to the fireplace or the piano. Be careful not to buy big puffy oversized seating. Your rug may work fine. Replace it last. I don't see any electrical outlets for lamps, but you need some. A chandelier on a dimmer will work for your ambient lighting, but you need task and accent lamps too. Shop for a piece of art 75% as wide as the piano to go 5" above it.

I'd make two seating areas. Pull sofa up closer to tv with ottoman in front of it. Then put the chair and bookshelf where sofa was for a reading area. The back of the brown sofa would be perpendicular to the back side of the kitchen wall. This would create a walkway to the dining area. Might work.

@ Rachel H We've created a layout for you with approximate dimensions from the pictures. So many options for colors that would work with those cushions and that rug! Warm tones of coral/ rust or even mustard would brighten up the room. Once you choose the colors on your chair you could add pillows that reflect those colors. You could place a couple of ottomans that can be moved around wherever required. As @My House says, you could add a slim console table and art/ Mirrours to the long wall by the door and create a nice looking entryway! We have made you another layout here. You can add or replace furniture and move them around to create your own layouts in interactive 3D designs here and also render your own photorealistic images here!