When hanging a mirror the first thing to ask is what will it reflect. You have a window in the DR and IMO a larger size piece of art in light colors would be my choice. BTW the dark wall in the kitchen does not seem to connect to anything I would not have it there and adding a chandeleir to the DR would be a good idea.

I would love to see the narrow black console that is currently by the front door moved to the long wall by the table. I think it would look great beside the kitchen. and it would anchor the mirror and possibly give you inspiration on what type of mirror to hang.

Perhaps one of these mirrors will work for you in your dining room?

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No mirror. You have nothing to reflect of any interest. And nobody wants to watch themselves eat.

OTOH--Thank you for posting a well-lit photo. You'd be surprised how seldom that happens. But, now, put a dimmer on those things! That's one well-lit room.

If that were my house, I would really want some visual separation between the Dining Room and both the Living Room and Kitchen. That's way too open for me. And I'd need some covering on that window. And I'd need some covering on that window; that blackness at night creeps me out.