Bear in mind that both Krk and Rab are *south* of Istria, so if you'll be staying somewhere in Istria, you'd have to backtrack. The drive from Istria to Sibenik will likely take you 4-5 hours along the highway (uninteresting), or about an hour, hour and a half longer if you take the coastal road, which is a really beautiful ride.

Stop by in Zadar on the way to Sibenik.

Split to Dubrovnik is about 3-hours drive, with a border crossing in and out of Bosnia. If you really plan to drive there after dinner, it will either be an early dinner or a very late arrival.

Two days in Dubrovnik is too much, IMO. Frankly, it's a very small medieval town, and once you've seen it, well... you've seen it. Rather make your trip to Dubrovnik a bit longer, spend a day, day and a half there, and drive back to Split to take the ferry.

Weather can be on and off in late October, you may have wonderful warm autumn, but you may get really cold wind as well... just bring clothes for both cases