It is were easy. We had been on the Costa Med. last year. We had to wait about half an hour, because first the passengers with flight connections were allowed to leave the ship. Customs procedure is very simple. You leave the ship and in the big hall you have to pick up your luggage. Than you will go to the shuttle bus in front of the station. The bus will bring you to Piazzale Roma, from where you can go to St. Lucua in about five to ten minutes.
Have a nice trip