I think your room is beautiful, warm and inviting as is. I think the fireplace is lovely as it is too. I'm wondering if swapping the positions of the sofa and matching (?) chairs would address the light and artwork issues you mentioned. You could put the small table with the lamp between the two chairs, bringing that light source more toward the center of room, which I think will illuminate the space a bit better. It's hard to tell from the photo, but It seems like putting the sofa on the longer wall would allow you to add a floor lamp at end of the sofa (the end near the checked chair) to bring light to that end of the room, while also leaving an unbroken space for art work on the long wall.

We have a similar issue in our family room. We have a bank of windows, a doorway that leads into our dining room and the space opposite the fireplace is open to our kitchen area. I am not a fan of TVs over the fireplace. I just don't think it looks good. We have windows on either side of our fireplace, so we really didn't have many options for TV placement. We moved to the home with the furniture (sectional and chair/ottoman) and we really didn't want to purchase new seating. I had a custom table made to run the length of the sectional and we had a sisal made to fill the entire space (which actually made the room appear larger) We just upgraded our TV from a 46 to 50 inch - we are considering a wider corner unit to better fill the space, but for now, it works. Could you still do the sectional, with the sofa table behind (as shown in your plan) and then have a chair (maybe swivel) in the corner (along the wall where the TV would be) -- similar to what we have in our room....

Another voite to remove the fireplace and hearth. Will you keep a desk area? If so, I would move it to the wall left of sliding doors, put the sofa table on the wall where the desk is now and the sofa against it. A lamp or two on the sofa table. Sleeper sofas are super heavy and sometimes not that comfortable to sit or sleep on. For comfort, a left hand chaise would be nice for TV viewing. With the FP gone, the TV could go to the left a bit and could sit on a small media cabinet. Rig sized correctly and a small round coffee table. ETA: After looking at photos again, I see that is NOT a desk area. If FP is removed, you could use that chest on the "new" wall with the new/smaller TV on top or hung above.

TV? It looks like the opening at the top should be further left. That makes room for the TV there. L shaped seating. Shown in this concept: Sofa/loveseat, two poofs, round coffee table, end table (lamp not shown), TV on a console table, area rug, tall plant. I did not measure the pieces so adjust size and postion. This concept swaps in a recliner or easy chair/ottoman. The TV is further to the right. A bookcase or shelves would be nice somewhere. If there's no TV these would still work.