Ferries from Croatia to Italy

See prices and schedules on the Jadrolinija website.
There is plenty of outbound transport from Bari--where do you need to get?

I am going from Bari to napoli

From ferry port to train/bus station, you may need to scope out the taxi/bus situation. Otherwise, you should be all set--I think bus is better for that route. I would check RometoRio to check (but verify the results by going to the provider's websites).

If you are traveling in June, July, or August, easy Jet has direct flights from Dubrovnik to Naples four times a week, for a cost in the neighborhood of 40 euros. Croatia Airlines and Vueling also fly between Dubrovnik and Rome; you can check their websites for dates and prices. Overall, a flight to Rome then train to Naples might be both faster and cheaper than the taxi-ferry-taxi-two train combination that you might have to take if you go the Dubrovnik-Bari-Naples route.

Another consideration regarding the ferry, sailings on some days are overnight and other days they're daytime. If you were to do a daytime sailing, you may have to overnight in Bari due to evening arrival. On a postive note, there's good bus service between the port and Bari Centrale train station.

Does anyone know roughly how long it takes between Venice and Rovinj via the Venezia Lines ferry? There website does not offer any information on transit times.

I took the catamaran from Rovinj to Venice, which included a stop in Porec to pick up additional passengers. Although I don't recall the exact times, departure was either 7:00 or 7:30 and we arrived in Venice maybe around 11:00. I think Venezia Lines posts its new schedules sometime around early February.