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.

squeakerd - it is really hard to get a perspective on the whole area but if this is part of a much larger area then I feel you need to first decide just what you want as the end result. Do you just want your entire area to be one open plan or do you want to break it down into visually defined areas within the open plan. As you have the area now, I don't feel any cohesiveness between your table and the sideboard, I think I would move the sideboard to the end wall, it looks more like it would belong there, even just by the shape of the room. Definitely a larger rug will define the space better - just be careful of any trip hazard with the door nearby - but before you decide on the rug, consider window dressings and whether you want things plain or introduce some bold patterns and what colours look best in the area. Artwork can go where your sideboard is now, but again think colours and impact of design on the whole area. It is all very well to build a room around one piece, but you need to look at the impact that piece will have on other items and what limitations it could cause. I would suggest you set aside some serious time to look through photos on Houzz, especially if you can find areas similar to yours, till you find what appeals to you, put the photos into your ideas book and use that to build your room. I have found this invaluable in the past and it has saved me many an expensive mistake.

Also take a look at Room and Board....they have several tables with different wood finishes or wood/steel/metal bases and a good selection of various tabletop materials. Also if you prefer a wood table, an area rug underneath the table could also help to break up all of the wood too.