No firm rule, but it should be properly proportioned. For example, this sofa was 90" wide, and we positioned a sofa table that extended just until the sofa back began to curve. In this case the top was 62" long. 48" would have been too short. This picture doesn't illustrate the sofa table we used. This one illustrated is too tall and too long.

I see your struggle with the living area, since it is small and right at the opening of the house. You do have nice elements to work with, like your big window and hardwood floors. You're right about painting the walls lighter -- the farmhouse look is airy, bright, and natural. Grey sofas are a good idea. Your art is too small, like shari13 said. It would be beneficial to have one large piece above the sofa that matches the look and feel of the furniture. Get a console table that is 50% larger than the TV on either side, and maybe mount the TV on the wall above the table for a cleaner look (of course, mounting the TV is entirely optional, but the console table length is considered a "design rule"). Getting rid of the recliner was a good idea. Finish the look with a nice, big transitional-styled area rug.

This is from over a year ago, all the decor and pillows are gone and we have started fresh, only keeping the couch.

I agree with Bev, it is both too tall and too wide. You should be able to see much more of the sides. And the couple of inches shorter should be shorter than the *back*, not shorter than the cushions.