First Time to Croatia!

Sounds great. The transport is really easy. See catamaran schedules on Krilo and jadrolinija websites. You won’t need a driver unless you have a specific plan like visiting a vineyard or something like that. The towns are tiny, so it’s not hard to suss out what to do.
I like your plan, though I could also easily be convinced to pick one island and stay longer.

There is a lot to Croatia that you would miss, but I think that your plan is good, as many
people try to cover the entire country in a short period and end up just spending too
much time on transport and less time on enjoying the beauty of the country.

I would say that 4 days in Split might be overkill. But a day trip to Krka Park would help
make up for not being able to go to Plitvice, and Trogir is a nice way to spend a couple of
hours. Otherwise, I might add a day in someplace else in the itinerary.

Thanks.

What other places would you recommend for a couple of days if shortening our time in Split?

If you arrive in Split, you can add TROGIR and SIBENIK the historic town near KRKA National Park, as daytrips They each only take about one hour to reach by bus or ferry.

From Split, Hvar Town is just a one-hour catamaran ride. Hvar has much more to see than Korcula, and, with four nights there, you can add the old city of STARI GRAD which is about a 45- minute bus ride from Hvar Town. The best beach near Hvar Town is AMFORA BEACH. While in Hvar Town, be sure to take the short hike (30 minutes) up to Hvar castle which has panoramic views of the town.

Korcula is a stunning, medieval walled-town that looks like a Hollywood movie set— except it’s real. You can walk completely around Korcula Town’s perimeter in about half an hour and swim in the sea by taking one of the many stairs down to the water. For beaches, you need to take a bus or taxi 3 miles to Lumbarda.
A couple nights in Korcula Town is plenty. With three nights, take an entire day to visit the Mikulics winery on the PELJESAC PENINSULA just a few miles east of Orebic. There is a small ferry boat that only takes about 20 minutes to take you from Korcula Town to OREBIC. At the eastern end of the town is
beautiful TRSTENICA BEACH. The Mikulic Winery and its tasting room are just a few miles east. We walked there and took a taxi back to the ferry in Orebic.

Dubrovnik’s fame far exceeds its size— it’s tiny. If you do stay in Dubrovnik four nights, take a daytrip to LOKRUM NATIONAL PARK, which is just a 15-minute boat ride from Dubrovnik’s Old Town port. You can easily spend an entire day here visiting the medieval monastery and its cafe, the ruins of Fort Royal, and Lokrum’s many beaches.
Another daytrip possibility from Dubrovnik is the ancient town of STON. Famous for its oysters, STON’s massive wall fortifications run for some seven kilometers and are more than three times the length of Dubrovnik’s walls.

Have a great trip!

I sort of like the length of your stays. It gives you good bases for day trips. Where? Look at Viator. You dont have to use them, but Its always a good listing of things to do from any location. Pick a few things that suit your interest.

You have time possibly for an overnight trip or two. If that interests you then Mostar or Kotor are options, but I wouldnt try doing either as a day trip and Viator probably isn't a good source for overnight trips. Post here and I bet you get suggestions.

If you reduced time in Split, I’d put those days towards the islands, but I lean toward outdoor activities and in the heat, swimming would be my main goal. It’s best to make your list first and then allot days. You could also insert another brief island stay if you are minimizing time in the main towns.