Short answer
São Miguel is the largest island in the Azores, stretching roughly 60 km east to west and up to about 15 km wide. It's big enough that driving from Ponta Delgada to the far east or west takes a couple of hours, so plan your days with travel time in mind. For exact figures, check the official Azores tourism site.
General information, not legal or tax advice. Rules and amounts change: confirm with official sources.