I would suggest shooting the architect, though I realize that isn't helpful..........

Turn the sectional to face the wall with two windows and add a sofa table behind it. In addition, remove the end table and turn the rug with the sectional, leaving it only under the front 1/3 of the seat portion and entirely under the chaise with about a foot or more extending past the two ends of the sofa. Replace the rustic end table with several "C" tables so people have a spot to set down drinks, etc. Put TV on a credenza 25% wider than it. That should be on the wall where you have the shelves. Get a tall piece of casegoods (bookcase or secretary) to put on the stairwell wall opposite the fireplace to serve as a visual counterbalance to it. Consider an art gallery traveling up the the stairs. Houzzers will prefer the personal photos in the master bedroom. If you keep the mirror above the fireplace, get a chandelier to replace the fan so there is something beautiful to be reflected.

First get the T.V off the fireplace put it a t the right viewing height on that huge wall where it belongs then either use the Besta system from Ikea or have a wall of storage and disply built there. Some window coverings , some proper sized art for the walls. Some lamps and hang your family pics in a hallway .

Thanks everyone for the great feedback. When we originally moved in we had the TV on the blank wall, but the struggle was that it was so incredibly dwarfed by the big empty space. It's also the only wall that doesn't have something on it architecturally, so I struggled to place furniture. The TV is mounted using a mantle mount, so when we do use it we pull it down to a normal viewing angle. I'm happy with it above the fireplace but would like to redo the fireplace to 1) get rid of the mirrors and 2) have the tv be less obvious.

I posted a mock up above that uses a wall unit (this one from crate and barrel)...what do you all think of doing something like this?

A substantial light fixture instead of the fan will help fill up the space and warm it up. And it will be an interesting reflection in the mirror.