We have just what you describe. Our dining room is in the same space as most floor plan's breakfast nook would be. It's 18x12 and we have a 8.5x4 farm table. I think it's very usable with a couple of caveats: 1.) Have two eating areas. We have the table - DH and I eat alone at the big table all the time. It's not like we have to sit at opposite ends yelling, "Pass the salt!" We also have an island with four countertop height chairs. 2.) Have a room that is multi-functional were a formal dining room might logically go. This is if you are concerned about resell. We had that concern, so my office can easily be converted to a dining room.

When you post a picture of a completed project and praise and mention the name of the person that did the project, it has the appearance of promoting that person, which is the form of SPAM. When you state that person is your "friend", it reinforces the appearance of SPAM. Let people contact you privately to get the name of the person responsible for the project design. For myself, I post an ugly picture of myself and make rude comments. New clients are not pouring in from Houzz and I have not been accused of promoting myself. In fact I have been accused of making architects look bad. I look at it as being honest.

Aww! No one else knows what to do either?😢

For ease of gettng in and out of the space, and because of the door on the right, the optimal seating arrangement for conversation and warmth is 2 facing the window, and 2 with their backs to the window. Is that enough? To make it comfortable for those with their backs at the window, extending the seat past the table edge on both sides is best. Getting a sufficiently long armless settee with a back would accomplish this, and they also sell dining benches and banquettes with back that are armless. But look for ones that seat 3 or 4 for optimal ease of getting in or out. A custom built banquette could be very lovely, and have storage underneath, and if made with a curve could give you seating for 3 on the banquette and 1 chair facing. But you'd have to deal with the windows plus it is lot more expensive than just buying a very nice upholstered piece. You need something more like a settee than a sofa for dining.