I think no one answered because my question was too open ended .. so to be more specific .. I have looked at some that are 30 inches high .. same height as table .. but I don’t know if i need to go higher like 34 or 36 inches ..

also would 54 or 60 inch wide buffet table be ok along a 13 feet wall, while the table is 11 feet?

also what Color will look the best ? The marble table color or the chair frame which is dark brown ..

I think 54" or 60" will look really skimpy with that long table against such a long wall.

But because it will not be centered against the table, because the first part of the table is across the kitchen door and then there is the light switch and the vent , so I can only put it starting at about 5 feet from the wall. Then from the other end only 3 feet of the wall be will be left, meaning will it look out of place then ?

It doesn't have to be centered on the table. I would center it on the wall.