Need measurements of the room, but in the meantime, I suggest removing all the shelves and use the niches for a small cabinet and mirror.

As is, you have a seating for 5 people, but a sectional is tight quarters for comfortable conversation.

Think you would be better served with 4 chairs, putting the ottoman in front of fireplace for emergency seating.

This arrangement except you will use swivel chairs.

I really like your neutral colors in the room. Very homey.

Agreed with all the above.
But a few tips and questions:
What’s your style?
Does a sectional work best for you?
I would:
Put a couch or sectional ( whichever benefits you more) facing the FP. Tv above. Love the cabinet idea for the built ins.
New chandelier. A rug. And coffee table.
The bones of this room are LOVELY!! love the character and detail. Floors are pretty too!!

facing the fireplace, will you be coming in and out of those french doors to the left? I'm assuming if you have the tv about the fireplace you are going to want your sofa facing it. You could do a sectional basically with the same layout as you have your couch with chaise. Once section again the wall and the other section facing the tv.

Or one sofa facing the fireplace/tv wall.

Move the current sofa to face the fireplace wall just to see how you like it.

I should have been clear… The furniture in picture is the old furniture. I have already ordered an off-white sectional in L shape

I do animal rescue so always have foster dogs. Thrown away many thousands of dollars in rugs due to dogs. 😩

Need help ! Do u buy a sectional ? Sofa ? How do I place them so we can see the tv above mantle ?

But, you already bought a sectional, so why ask?