Mid October, the weather can be lovely, but you can hit a wet patch too. Take a look at the historical figures at http://www.weatherbase.com/weather/weather.php3?s=25431&cityname=Dubrovnik-Croatia&set=us
In Dubrovnik and Hvar town things will be pleasantly quieter, but in less popular places, some cafes and restaurants will have closed for the winter. Which doesn't mean you won't be able to find somewhere for a coffee or a meal, just that there will be less choice.
As to the ferries. By then the Dubrovnik - Hvar - Split - Rijeka ferry will have stopped. I don't know about the hi-speed ferries Dubrovnik - Hvar. As to Split - Hvar, they run all year - a fair number of people live there, not just people involved in tourism.