Rather than focus on the wall of windows you might first paint the walls a mid-tone or darker which will do wonders at warming up the room. You may not then need to dress the windows at all. You have very valid reasons for leaving them uncovered. Window coverings for that expanse of windows will be very costly and there are many other ways of warming up the room. If you are interested in having plants to soften the space you might consider a couple of Dieffenbachia as they are fairly inexpensive when small and grow quite quickly. Of course there are warnings about the toxicity but I've never had kids or pets eat them and I have read that warning is over-rated. I've had one grow to over 8' tall and seen them much taller than that. They actually do better in lower light situations and mine did well in a north-east window. Whatever plant you choose you could put it on a pedestal when small for greater impact. I'm not a fan of accent walls so wouldn't advise painting the fireplace wall a different color. Too often accent walls don't work as intended for interest and I think there is enough going on in this large room so that keeping all walls the same color would be best.

One thing to do..........The short wall to the right of the coffee bar is not a supporting wall, and could be ripped out when you rip out the sink and cabinet. This would eliminate one of the "nooks" and open the room up a bit. If you truly do not need the upper platform for anything useful, I would just put decorative doors over the space and close it off. Maybe sometime down the road you will need more storage space and it will come in handy.

Consider what might be most useful to you and if you want matching configurations. Storage, library, displaying, desk, etc. No matter what you decide, I would reduce the depth in half by drywalling as I think it will provide lots more options. There may be a need to redo fireplace moldings and even mantle if going with builtins.

Our Great Room couch has the back of the couch facing the entrance, with a glass console and lamp on it. The designer was not necessarily right, so move everything around (use heavy athletic socks if you don’t have the sliders) and try the other layout. You can add more color with pillows and new drapery panels. If you have any extra money, you can consider a more colorful rug to replace the matching one. Even a 9x12 can be only a couple of hundred dollars but would make a huge difference in the look of the room. Do you like navy? Red? Orange? Greens? Add some pillows and solid (or subtly designed) drapes and your room will light up. JCPenny has great prices on drapes, as do other online companies. Longer, fuller drapes will really enhance the feel of the room. The art work issue has been addressed very well by others. Just try the other furniture arrangement and send a photo. Lots of pros here can help you assess how it looks.