The French doors at the two ends of the room could be removed to make room. If you have to allow for them to open you'll have less space for the sectional. I would float it in front of the FP. You need a large piece of casegoods or a long console table and big art gallery opposite the fireplace as a visual counterbalance to it, and you need to leave walk space behind that wing of the sectional so both doorways can be accessed. Subtract depth of the casegoods (12-18" for a console, secretary or bookshelves) and the width of the walkway (36" or a bit less may work) and a small passage (18-24") between the sectional and the fireplace hearth so you can squeeze in from there. That should tell you what length the sectional can be. I estimate about 7 feet for the wing perpendicular to the FP and as much as 9 feet for the section facing the FP. If you can get a reversible chaise sofa you'll have more options. It won't be as large as a full sectional, but it will be more conversation friendly when you have guests because you can add a pair of chairs to the room. Gus Modern makes a nice apartment sized one.

Looking at it from every angle, the clock does look lonely there, and I really don't think paintings are the ideal solution. You need a lower piece of furniture to tie the clock to something solid, and a narrow table is the best idea. Perhaps you can put some of the items from that high shelf, which right now diverts the eye from your living spaces, on the table. I also agree that the three pictures lined up on the stairs don't look right. Since you like them there I would suggest that you hang them much lower, at people height.

Pretty room. Can you post a pic taken from the corner pointed at the bare wall and the french door wall? Without seeing the whole space, properly hung art is always a good choice. Perhaps a console table. A large floor vase with tall filler is also a good way to add interest to a bare wall.

I really like your remodel. love the kitchen cabinet color. One idea for that long tall wall is to perhaps add a tall cabinet to the left of the sofa, possibly an open bookcase or a tall closed cabinet, depending on if you need storage or perhaps a place to show some of your treasures you might have or books, a large piece of art above the sofa and then to the right a side table with a tall floor lamp. the floor lamp will balance off the tall cabinet on the left and the sofa and art above will connect the middle part of the wall to the two ends. a few ideas on tall cabinets....