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:

No, I don't think it would look awful. I love big art pieces. The important thing though is do YOU like it? It's your home and it's important that it please YOU. Looking at your picture, I'm wondering if the art above the sofa isn't a tad big for that wall. (I really like it, btw.) Usually, the eye appreciates some breathing room around art. If you have painter's tape, try taping out that canvas' size above your couch and see just how much wall it covers. That might help you visualize its negative space better. Good luck and enjoy the process!

A sage green would probably go with a dark blue. Also greens in the lime color would work. I would pick a blue that is much lighter that goes well with the dark

Deciding if the trim should be the same color as the walls(white chocolate) or should the trim be super white for a contrast for my living room, dining room and entryway(all on the same level)