Croatia itinerary - 11 nights

Sounds like a nice, non-rushed pace. If you didn’t have day trips planned for Hvar and Split, I might say you could do with 2 nights each.

I am no help on busses, but here are the links for the island ferries - use whichever suits your schedule and desired arrival harbour. I used Jadrolinija Spit to Hvar and Krilo for Hvar to Korcula.
https://www.jadrolinija.hr/en/about-us/ships/ferries
https://www.krilo.hr/en/

Also look at Croatiaferries.com. It gives you a comparison between the two companies texastravelmom has provided above.

I have friends in Budapest that pack up their 2 kids and head by bus for the Croatian coast every summer so it sounds like the bus is a good idea ... but it is, what? 6 or 7 hours?

You also might want to check on flying from Budapest to Podgirica on Wizz ($40 to $100 depending on your luggage)

Takes about an hour nonstop.

There is a lot to see on the 3 hour drive from Podgorica to Dubrovnik (Kotor, Herceg Novi, Perast) ... then you do tge tour you have planned, but in reverse.

You can do it by bus or I know a company that can arrange the day with a driver.

You might look into taking a little time and visiting Montenegro since you'll be just north of there.

We were in Croatia and Montenegro in June, and want to go return. And we also want to also visit Slovenia.

I’d either skip Korchula or add a night. It’s beautiful but IMO not worth the hassle for essentially a day trip. The “fast ferry” from Korchula to Dubrovnik was extremely unpleasant so that’s not a great solution IMO unless you like closed spaces, tobacco smoke from the crew and a vomit inducing ride.
The normal ferry is great, but it’s not a quick trip. Again, just too much hassle for one night.

Split just didn’t warm my soul at all. YMMV, but it had a big city, gritty, working city vibe to me. Can’t comment on Trogir.

We spent a couple nights in Rovijn and did a day trip to Pula. Rovijn is beautiful, especially at night when the crowds thin, but it is touristy.

3 nights seems perfect for Dubrovnik. Btw, flights from Dubrovnik to Rome or other connecting cities are cheap and convenient for you flight home.

We love Split! I think it's a beautiful city architecturally and has a wonderful location on the Adriatic. I love the way the city developed in/around/through Diocletian's Palace. So interesting! We hired Maja Benzon, recommended by Rick, for a 2-hour private guided tour of Diocletian's Palace and Old Town. Loved the Ethnographic Museum. We spent 4 nights in Split which included a day trip to Hvar Town and a day trip to Trogir. So I think 3 nights is perfect.

With your 3 nights in Dubrovnik, you could take a trip around the Bay of Kotor in Montenegro. You could hire a private driver which is easier so you can enjoy the scenery and not worry about finding parking in the small towns. We visited Budva, Kotor, and Perast. Enjoyed all 3 but Perast is our favorite.

We rented a car for our trip. Driving is very easy in Croatia, in case you prefer to drive instead of depend on buses.