I love the clean, uncluttered look of your home and you've made some great furniture choices. My first thought, though, is that I would try to rework the sofa/sectional placement. It really is unwelcoming looking to me to have the back where it is facing a wall, when it could be oriented to look into the room and out the windows. It seems like if it were placed in the corner under the stairs that it would feel open and invite you to come in and sit. I'd hate to be cooking in the kitchen and have the family or guests with their backs to me. If you are having a TV in another room close by, do you need one in that room, too? If, so placing a 70" unit will probably only work as you have it. But, to me, it's not going to look like a living room but more like a movie theater, which is fine if that's what you're going for. It seems like it won't be a cozy conversation area, though. I might actually flip the rooms and put the dining room where you have the sofa now. I was looking at lights used with dining rooms and ghost chairs and saw this, maybe would work in the living room? Kind of fun. don't know if it would look as good without the colored walls though. And I thought something like these were interesting to consider for over your table:

I agree, there is not much to be said without more pictures, but looking at what we have, and not knowing the size of your starbust mirrors, I think you could hang them to the right of the TV to fill up approximately the shape I've indicated below. Second point, look for a striking rug that has a similarly natural, organic feel. It could continue your neutrals theme or introduce colour, but I'd definitely go for some kind of organic pattern -- not a geomatric design. I've just come across this one and I love it. https://www.overstock.com/Home-Garden/Hand-Knotted-Roth-Abstract-Pattern-Hemp-Rug-5-x-8/9912730/product.html?refccid=CPCHMYDRCEE2WRKCR4625KZO2Q&searchidx=337&keywords=&refinement=material%3ANatural%20Fiber

Not every wall needs to be decorated. You could easily put a large tall plant in the corner next to the window. Home Depot usually has good ones for not too much. Any of these would work well. Every room needs a plant. They're great space fillers without looking contrived. They really cozy up a room.

Just moved in to our rental, they won't let us paint so looking for help with window treatments and pictures. The room open to the dining/sitting room