Getting to Lerici
The closest airport is Pisa, which has connecting flights from most major European cities so if arriving via connecting flight, it would be the most convenient. Otherwise, there is Florence, Genoa and Milan. Milan has plenty of direct flights from New York but will take 2 1/2 hours driving to arrive to Lerici or 3 1/2 hours by train.
If coming from Pisa, a rental car or taxi would be the quickest option. From Florence, Genoa and Milan, a rental car or train would be be the best option. All of this depends as well on what you will be planning to do before and/or after the wedding. If planning to go around to see some different places and take advantage of being in Italy, a rental car would probably be the best option as it will give you the most freedom, but you can certainly get around by train to pretty much all of the cities and areas you'd like to visit.
Pisa
Pisa: The Tuscan city is about a 40 minute drive from Lerici and there is plenty to see aside from the leaning tower, including the last public work by American artist Keith Haring before his death- a massive 10 x 18 meter mural titled Tuttomondo painted in 1989
Florence or Firenze
About an hour and a half drive from Lerici and an hour by train. What can I say about Florence? If you've never been, then go. If you have been, then go again. It's a beautiful city full of art and history- the birthplace of the Renaissance and to some of the most famous works of art and architecture in the world by people like Leonardo da Vinci, Michelangelo, Brunelleschi, Vasari, Giambologna, Niccoló Tribolo... and the list goes on and on.