Since you've tried the over the counter method, I would agree with Bobbi. Hire a pro. Those sinks are so pretty refinished to their original state and a pro will give you a finish that will last the rest of your life. If you can't find anyone listed in the phone book, ask around at a hardware store.

You may have to identify the source of leakage and apply appropriate sealant. For granite joints the best solution would be metal paste. Clean the existing sealant and put a fresh one for better results. Thanks Nitin CORNERSTONE DESIGNS Bangalore

Totally doable as long as the island is not too bulky. And of course if the circulation space around the island is at least 3'-0" wide. You don't need too much space to move around in a kitchen because you should be able to pick up a hot dish and put it down on another surface without having to move too much. 12'x14' is a large size and a work island would possibly make the space more practical to use. In the pictures attached, the work island is only 2' wide but 4' feet long

Steel inlay will increase your problem manifolds. Have suggested an alternative on your duplicate post. Thanks, Nitin Cornerstone Designs, Bangalore