How to reach Sicily by sea
There are two often used ways to reach Sicily by sea. Firstly, you could catch a ferry either from Napoli or Civitavecchia to Palermo. Alternatively, you could fly to Malta and catch the ferry fromMalta to Pozzallo. It takes about 15min by taxi to get to the port from the airport and the ferry usually takes an hour and twenty minutes to cross to Pozzallo. Caronte From Salerno to Messina. TTT lines from Napoli to Catania.
Tirrenia once a week sail from Trapani - Tunisi. On manday at 10.00 AM leave Trapani and arrive to Tunisi at 18.15 PM. From Tunisi leave at 9.00 Pm and arrive to Trapani at 07.30 Am on tusday.
The travel is comfortable and the ships are truly pleasant with their halls, bar, restaurants, self service, swimming pools etc..... Look here.
The islands
Sicily is surrounded by islands. Egadi, Eolie, Ustica, Pantelleria, Linosa, Lampedusa. You can reaching these islands within 8 hours sailing. 
Good trip!