My family has enjoyed Croatia a lot. Very friendly people, usually willing to make conversation, and very responsive and appreciative of positive opinions about their country. Don’t stay in the tourist bubble, get out and about and meet some folks. As an icebreaker, try complimenting their football team and their performance four years ago. (You’ll see the distinctive team gear for sale everywhere.) Do not ask them about Serbia and their history with their neighbors unless you’re prepared to navigate a prickly subject.
I see you’re down in the southern half of the coast, between Dubrovnik and Split. I personally prefer the coast a little farther north, around Zadar. It’s less touristed and resort-y, and noticeably less expensive as a result. It sounds like your itinerary is pretty well set, but if you decide you like Croatia and want to go back, there’s a lot more to see outside the usual destinations.
As far as things to do, if you can find time, a ferry trip out to the islands is recommended, even if it’s just a cruising tour without landing. The terrain is phenomenal and breathtaking, with incredible views everywhere. And if you’re interested in getting out into nature, Krka National Park is an hour from Split, and is fantastic, well worth the visit.
Regarding what to eat, as you’d expect from a country with a long coast, the seafood is great almost everywhere you’ll be going. Further inland, there’s a great tradition of meat, but on the coast, fish rules.
You’ll find the food vaguely familiar, Mediterranean in character, while still being its own thing. Visually, it will strike you as simple and rustic, but the flavors are strong and hearty. The trick, again, is to get out of the tourist bubble. Go to a small neighborhood and find a hole in the wall with a wood oven on the patio. Look for the word “peka,” which refers to an enclosed vessel used for hot-coal cooking. Some peka places will ask you to make your reservation and place your order in advance, because they will serve only the freshest possible octopus or fish, and they will procure only as much as they have reservations for. Even if you don’t find a convenient place offering peka, don’t be surprised if the “menu” is the waiter holding out a tray of just-caught fish for you to choose from.
If you see anywhere offering Pag cheese, try it. It’s a local specialty produced on one of the Dalmatian islands, and it’s delicious. Also, Croatian wine is pretty good, underrated on the world stage in my opinion. If the opportunity to taste some comes up, definitely grab it, and plan to take some bottles home with you. Ditto the locally made olive oil, which is absolutely world-class but doesn’t get the same level of attention as the Greeks and Italians (or even the Spanish).
Very envious of your trip. You’ll have a great time.