Upholstered vinyl chairs with nailhead could be very cool. If you have a tight squeeze on the one side a bench is a nice addition and try two more prominent head chairs of a different style than the side chairs if you are not doing a bench. Bring home some swatches and play. Thinking a light ivory or cream....Nice table!

I sense that you like an eclectic look. I would go for grey walls. A funky chandelier. If you want new chairs you could go with mix and match, or you could just reupholster the ones you already have. I like the idea of having chairs on both of the long sides but not on the ends. The legs of this table are the best part and it is nice to show them off.

Any recommendations for wall decor / art?

I love original art and lots of color! Especially the abstract resin glossy look! Good luck to you - you've got a great start!