I'm going to disagree with advice to paint first and hold off on reupholstering the chairs. You say you've been waiting three years to do this. Selecting fabric can take a lot of time--esp. when working with an open floorplan where you want the colors/fabrics to flow from room to room. You have some lovely fabrics to choose from that can be incorporated into your space in a variety of ways--or even into the adjacent rooms. I recovered my DR chairs last year and am so glad that I did. Mine also were hard and uncomfortable--which you said yours are as well. One thing that was important to me was the fabric not only coordinate with my DR, but my LR since I planned to occasionally move the DR chairs into the LR if I needed extra seating for a party. Personally I found a stripe to be the most versatile choice. I do also agree that you are more likely to tire of a floral or find it more limiting as time goes on. To me, your ivory will always read more formal due to the sheen of the present fabric--not so much the color. If you still like the floral, I would again consider using two complimentary fabrics and use the floral in smaller doses. For instance, you could do the host chairs in floral and others in stripe or solid, or do different backs/fronts as I suggested earlier. Or bring in your floral fabric in a less permanent way via a table or buffet runner. Calico Corners is also really good with suggesting complimentary fabrics. It may be worthwhile to bring in a swatch of the valance fabric and ask for advice on complementary fabrics.

Three types of seating at one table, especially when there is a patterned rug and molding details is much too busy imo. The bench seating also doesn't allow you to pull it out to sit and push it in be the right distance from the table, so someone is scooting in awkwardly. I think you can use upholstered chairs on the ends, if you have room for it, and different ones on the sides. But from the photo it looks like you don't have room for chairs on either end. The legs of the chairs need to stay on the rug when they are pulled out to sit down. In that case, just use four chairs on each side of the table, and leave the ends open.

Correctly made Windsor chairs are the strongest wood chairs ever made and will take whatever the family can dish out, and go with your decor. There are a lot of poorly made ones, its important to get through-the-seat and bows, bore and wedge construction. Good ones will be around $ 300 to $ 400 apiace. https://www.lawrencecrouse.com/side-chairs/ I have a set of (4) Black Sides in my warehouse if you are in the locat Washington DC region.

I will never again buy dining chairs without stretchers. They're the cross pieces between the legs. In my experience, dining chairs without stretchers get wobbly very fast. Your pictures are hard to see because they're so small. Better to post them individually on the post or in your idea books.