I would definitely get rid if the mantle. It is too high above the fireplace surround. I agree that a large piece of art or your tv above the fireplace would be great. I really like that green we can see in the background of one pic. I would bring that into the living room and dining room. More substantial draperies would help and a pattern might be nice as long as it is something you love and won't tire of in the near future. One other idea would be to add a good-sized area rug in the living area even though you would be putting it over carpet. That could bring in enough color and pattern to pull everything together (still get heavier draperies though). Add a throw over the back of the chair or couch, a tall vase with flowers or tall fern fronds on the hearth, bowl with fruit or veggies on the table and go from there. Show us what you try! It is going to look great!

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:

Before adding art to the walls you might want to finish getting your furniture. It seems that you especially need tables/lamps. Overhead fixtures are the worst for creating harshness and making everything and everyone look bad. Are you adding chairs? Have you considered a more colorful rug? Once these things have been determined it is time to think of art, You should not just go out and buy stuff for the walls, Take it slowly and wait till you see things that you love or have meaning. The decor can be things other than " pictures". It can be plates, baskets, funky objects, wreaths, etc.

Essenzza ignore issues of taste and home clutter. There is not one taste or one type of good style, and home decoration should be the artful arrangement of the ideas and functions YOU want in your home. The issue I find, with family photos, is that small framed ones wash out when viewed from far away, and there is a limit to how many large family photos you want displayed prominently in your home and where. My husband, god bless him, insists on large family photos on the shelving unit across from our bed in our small bedroom. His family is constantly staring at me! He finds it comforting, I find it a little less than restful. But I can live with it. So that's an example. I'd feel the same way about a large family photo in a living room or family room over a fireplace. It's just too much like "The Smith's survey the room!" On the other hand, slightly smaller in a less prominent space surrounded by some more casual shots, it might be "Remember those happy times when we were all together!" But anyway, I think you are talking about a collection of smaller photos. The issue with those is you can't really see them unless you can get up close to them, which is why I would not put them on either side of the TV. Given that parameter, I would put up a display shelf under the "Eat" sign in the dining room. Then I would either put the stuff on the dining room credenza on the shelf and put a collection of family photos in a mixture of nice frames on the credenza, OR put the family photo mixture on the shelf. I have seen both done well in dining room inspiration photos which you could probably find by googling "dining room family photos arrangement on shelf" or some such thing or by searching Houzz photos. That way people can stand up close to the photos and look at them if they want, and yet the montage still looks good from a distance. Again, I would shoot for more casual photos, not a dominant set of people staring straight ahead. I have a two-photo frame with a picture of both my grandmothers staring straight ahead on a credenza in my dining room, along with my tea set in an arrangement. That level of personal display is not overwhelming and doesn't dominate the look of the room and they are accompanied by other decorative elements so their steely gaze is softened by that somewhat! :)