Kennebunkport is 35 minutes from the nearest airport, so renting a car is a great option. This is particularly true if you want to explore the area/coast during your visit. However, Uber/Lyft are available in and around Kennebunkport for quick (and sometimes not so quick!) transportation. Transportation will be provided in between St. Brendan's Chapel and The Colony Hotel for the ceremony and reception. If you are staying elsewhere, you may find your own way to/from the ceremony or meet at The Colony Hotel beforehand to catch the group transportation.
Since this will be peak season in the Port, it would be a good idea to make a reservation if you do not want to have to wait. That said, not all restaurants do take reservations, so please call ahead if there is somewhere you'd really like to try (see Things To Do page).