Not a crazy idea at all, I've found that driving is very civilized, definitely if comparing to Italy. Drive to Ancona, take overnight ferry to Split. If you want to visit an island, you could opt for Hvar where you can catch a ferry back to Ancona. There's quite a few connections between Italy and Croatia, but in October they will run on winter schedule (less frequent). There's quite a few comparison sites out there. Temperatures in Oktober still quite nice, but rain can be expected.