I can't speak regarding exact sizes or dimensions...the size of things you should or should not get but.... I can give some thoughts on overall layout and placement of furniture.

First, I'm assuming from the photo that the kitchen is attached to living area? I seem to see kitchen sink in foreground of photo?

Either way, for a long narrow room and where you want a couch/seating, I personally think it's important to try and 'soften' the room...because it's long and narrow, whatever you put in the room could add to that boxy or straight/hard feeling. When I say 'soften' I mean... I like furniture at slight angles...or not perfectly straight.

I never press a couch directly against the wall. It feels stiff and feels like lack of air flow ('chi'). I would pull couch at least 2" from wall.

Also, instead of one long (stiff/straight-looking) couch, how about a loveseat, and then 1-2 chairs on either side of the loveseat or couch, turned at a slight inward angle ...so the loveseat and the two chairs almost create a very soft C-shape? I'm also a fan of round side tables vs square ones, again, to help 'soften' hard lines. Put a round side table between the loveseat and one of the side chairs.

Another option is to add a pedestal light with a globe lampshade, at either end of the couch.

A tree plant in one of the corners of the living area (say one of the corners by the entry door) creates a focal point, adds 'life' to the room and vertical interest.