Will this be the main TV room, or is there, e.g., basement space for TV watching?

There is an area in the basement, however, we will mostly be in this area.

If room I would position the sofa across from the fireplace wall and mount to the right of the fireplace at appropriate viewing level. A swivel chair on either side of the sofa or where the two chairs are currently. My neck hurts just thinking about viewing the TV from the side angle and tilting my head up. Large fireplaces and big screen TV’s do not mix comfortably.

agree ^ sofa across from fireplace. Leave the windows open with chairs in front rather than hiding with the sofa. A Sofa table behind sofa as a nice divide. a larger area rug, centered on the fireplace to fill the area from built ins side to side. look for low back swivel chairs.

Do you think there's enough room for the sofa to be straight across and not bump into it when walking to the kitchen?

To me, it looks like the rug isn't sized right. I think a larger rug could tie what you have all together.

How big of a sofa should I get?

The room requires a much larger rug for the space.

looks like there should be room, although having to guess at a few of the measurements on your diagram.

Try placing the couch facing the tv…then add one swivel chair on each side of the fireplace….far enough back to view the tv as well…if there is room add a long table behind the couch with a bend or chair(s) behind

That table will bea great place to sit and have a snack or meal watching tv

Sofa or sectional and how big?

Great place for a snack or lunch

My fave spot for lunch or snack