Hi there! You have a tricky layout, for sure! So many windows and of course the door, where you will need to keep some clearance for passageway. And multi-purpose to boot!

You would be amazed at what a simple de-cluttering and a fresh coat of paint will do to your space. I would love to see this area painted a warm but chalky (not Ivory) white, such as Ben Moore Simply White.

Modern curtains and some comfy sofa pillows, as well as a round coffee table, will make this room look brand new.

I think your furniture is in the best possible place, all things considered. Mounting the TV to the wall (exactly where it is) would give a cleaner look to that area. Then mount a ledge below it to keep PVR box, etc. on. Keeping the wall below the TV free of furniture will look less cluttered and a little more like the TV "belongs" there.

Use the shelving beside the FP to corral other paraphernalia, all in matching bins or baskets. Reserve the upper shelves on each side of the FP for decorative objects, rather than storage.

Rather than a mirror over the FP (which is t reflecting anything attractive), find a modern piece of art in bright colors so that it will really pop against the white brick and walls.

Seat cushions (Pier One has them) spread along the FP bench will make your overflow seating more comfy. Keep a set of nesting tables next to the sectional on the FP side - you can bring out the smaller one when needed.

You could hang a decorative mirror on that wall beside the door. It would reflect the FP and possibly the art on it, as well as bounce some light around this part of the room.

Finally, I just don't see a good spot for the treadmill. Is there anywhere else you could place it? It will really detract from all your efforts to pretty up this space.

Hope this helps. I'll have a look for curtain and pillow ideas - back in a bit!