Nix the bench. Terrible for people to sit on and once on it, it is never in the right position, so floors get scraped up. Picnic tables outside fine but not in house. OK, can you remove the seats of the chairs and recover them with a nice leather look? That is simple to do. Turn the chairs over (maybe you have already done this so forgive me) you should see some holes and deep in the holes will be screws. Those screws are holding the seat in place. Remove the screws and seat will come off. Then it is simple to recover. Need a sample gun (electric) some fabric and watch a youtube video and do it yourself. You can pick any fabric that is washable you want. Some of the new Sunbrella fabrics are really nice too and they wash. Slip covers for these chairs I don't think will work, to say nothing of the cost.

I feel your best option given the space and wanting a sideboard or console of 15" to a tad over for putting things on would be 45 to 48" with an extension or table with leaf(s) if you will when needed. Keeps the room elegant, but then you still have the space if you need for larger groups. 60 is way too large for the room. It will be way off scale and not look elegant with your light fixture, a side console or narrow sideboard. WAY too crowded.

I think the wood color in the space works best. My kids did eat at the table: 3 boys very close in age I worked as a nurse for years and my husband is a airline pilot so I was often alone. I think I wasn't like I am today though so, no harm to foul. I have family gatherings now that my MIL has passed as she loved it so I didn't have them. I find I'm ridiculous with my linen furniture and so on and everybody running crazy with dirty hands, running with food, chasing each other and so on. Yet, I have a glass of wine (or two....) and let it go. Probably a bit less controlled with about 6 little ones running all over the place that are not mine, but are relatives so..... I say what ever works for you..... go for it. I didn't have a lot of, "nice things" that I put a lot of time and energy in to back then so it was not the same to some degree. The older I get the more persnickety I get. Sad, but true :(

Depends on how often the grandchildren come by. If occasionally: place a plastic cover over the table of your choice whilst they are there. You might as well cover all the other light furniture with a nice washable cover, for kids are champions in getting things ruined, especially new things. If the grandchildren visit more than once a week: good luck with your off white furniture. Hope you choose leather... As for a color of wood: anything you like. As long as that same color is coming back someplace else, so it doesn't stand out too much. Frames in the same color for your artwork would do the trick. Or pots for plants. Even pillows on the couch. Good luck.