I like your idea of a round table because it looks friendlier and seats more people. The color doesn't have to be an exact match to your kitchen cabinets, and if you can keep it in the ballpark that's fine. Matchy-matchy can be boring. A rug is a splendid idea, and I suggest you make it on the large side, after measuring carefully. Can you move the table and chair further away from the kitchen to leave more room for a good-sized rug? I would also suggest two beautiful runners in compatible colors and styles for either side of the island to break up the large expanse of wood.