Cocktail/semi-formal attire, think summertime gardens and island vibes. The weather on Mackinac in early June can still be cool, so maybe consider layers as appropriate! The ceremony will be held outside weather-permitting, and dinner will be on an outdoor patio with heaters if necessary and will be rain-protected just in case.
That is completely up to you! We will be staying on the island the night before and the night of the wedding, but the ferries run all day from both St. Ignace and Mackinaw City, so it is entirely up to you if you'd rather stay on the mainland (which is often much cheaper than the island accommodation options!) Dinner will be over by 7 pm, but we do plan to go out to the bars afterward so if you'd like to join us just be mindful that the last ferry off the island is at 9 pm!