Do you have any tile left over? Here’s a video on making a mosaic table top for a breakfast nook.

https://www.hgtv.com/videos/breakfast-nook-0114413

Bad idea. You'll be building a U-shaped banquette that seats 6 or 8 people, but leaves only enough room for a table that's less than 3 feet wide. They can't eat on a table that small.

I would hate to be the schmo who gets stuck sliding all the way around to end up sitting against the window.

Banquettes suck unless you sit on the end.

I'd put a round table in there with a chair in each corner. Even then it'll be tight and the people in the chairs near the camera position will probably have to get up and move to let others around them.

I think you have room only for L shape seating. I'm figuring minimum 20-in seat depth.

Benches and booths are one of those things that look charming and cute, but are a huge pain to actually use. They're fine for kids, but getting in and out of them is a hassle as is cleaning. If you're set on it, I would only do an L or one bench.

A small round cafe table and two chairs would be nice there.

A small rectangular table and two chairs.

I wouldn't get a corner bench. There's a whole lot of scooting and kids sliding out under the table and general awkwardness with a long L shaped banquette.

With a family of six, I'd try a rectangular table pushed against the far wall, under the triple window and a basic long bench on either side. People --especially little people-- won't be trapped because they can swing their legs over the bench and scoot behind.

My mother in law has a small dining area and has a bench up against one wall--it's actually very comfortable because we use the wall as a back rest.

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I think the general calculation for table overlapping an armless bench is about 4". make sure the table has either a trestle or pedestal base.

Ballard sells banquettes. https://www.ballarddesigns.com/furniture/dining-kitchen/banquettes

We tried out a small upholstered L shaped banquette for a while. I found it on craigslist.

I think a bench would be VERY cool in that space!

If you have another larger dining space, you could use that space for when the entire family is at the table and save this space for when the children are elsewhere and it's only the two of you.

You'd probably be better served to not build in the benches in a "U" shape taking up most of the space; however, you might consider a "u" shaped bench -- a window seat built only at the window end of the space (seating two) and rounding the two corners -- but only enough to seat two more. Then you could have two wheeled chairs for the adults.

http://www.charmcityagent.com/build-a-window-seat-using-stock-kitchen-cabinets/

This would make this nook a lot more attractive -- not only to the two of you as you eventually become empty nesters (less cluttered feel) but also to potential buyers should you ever decide to sell your home.

Choose a wheeled table for easily moving it out of the way for cleaning.

I am not sure you can sit six in a U-shape this size...one has to figure in the space needed for knees/legs and the fact that two sets of knees/legs cannot occupy the same space. You should probably make the effort to mock up the U in the space before you commit time and effort to build especially if the goal is seating six.

You might want to plan for a chair at the open end. Check out the 'morgue drawer' threads for storage ideas: GW discussions--morgue drawers.