You can try putting sofa in center of room in line with the door facing the wall, and put the tv in a cabinet on the wall. Put a couple chairs there on the sides. Different larger lamps, replace the fan with a fixture light. The rug is too light for the room and furniture. If you use on get it darker and larger so some of it goes under the furniture

Same problems with my walls, is the yellow - tan color...it looks dingy by today's decorating standards. I would paint the whole room blue or gray, cover your sofa with a white cover, same with the chair. You need one more panel on the window to even out the look of the window. The fireplace, if it stays, needs a long tall mirror. I does seem like a generous space, and I'll bet it will be great when you're done with it.

Nix ceiling light. Lights in each corner much more flattering in a living room. Lights in corners need to be bigger. Yes, do look for some wall art. Wait until you find items you really love. Either make them, find at a local gallery, or art.com. Bring living room colors into art for a unified look. Several large pieces behind the couch may work well.

If this is to be a "man cave" does he really care about the fireplace? It might look nice in the dining room or in your bedroom. Since nothing is facing it, why bother? I doubt you're heating the room with it.