For chair scoot and sit space, I'd follow the guidelines for a rug - 4' all around. Then you want to be able to navigate around the table while people are seated, so add another 18" all around. Are you locating the table at the end of the galley? Maybe you could use a banquette on one side or in the corner https://www.houzz.com/photos/3rd-street-bungalow-traditional-kitchen-austin-phvw-vp~214425

Try wood and glass. Consider hanging the mirror vertically and about 5" from the sideboard top. You could also move the table under the light fixture, change it out for a chandelier, and put the sideboard and mirror on the clock wall where the mirror could double the chandy which should hang 36" or less above the table top.

If you think hitting the lamps could be an issue, just move them a bit and add some low accessories (opposite sides to pic below). It's better to have a bit larger lamps and with your ceiling height anything shorter would look skimpy and they don't overwhelm the bedside tables once you balance with something above the bed. Just a thought...if you accessorize your bedding with some soft colors, they will also help to compliment the glass and crystal. You could even change the hardware to a silver.

Hi Jennifer K, thanks for your comments. The photos you have posted are really lovely but not really suited to our environment and house, which I know is impossible to tell from one photo. We have built a modern farmhouse on 10 acres. That room looks out to beautiful green countryside and the river below. The dining room is a bit of a feature and is completely different to the rest of our relaxed lodgey style house but I don't want it to be too modern, if that makes sense. The photos have given me a few ideas so thank you so much for your help!