A couple of years back, I did a road trip in Slovenia that included: Logar Valley, Kamniska Bistrica Valley, Kamnik, Vintgar Gorge, Lake Bohinj, Lake Bled, Vrsic Pass, Bovec, Kobarid, Postojna Cave, and some other places. I had a terrific time, mainly thanks to the fantastic scenery. I'm now looking to go somewhere with similar scenery for a week in the first week of April (Easter period).
My key requirements are daytime temperatures over 12 degrees centigrade, not too much rain, and options for 2 or 3 half-day hikes (up to 12 KMs each). I have no interest in archaeological sites. Since I'll be renting a car, I'd prefer to fly into and out of the same airport.
One of the three places I'm considering is Northern Croatia (flying into Zagreb). I still have to research and prepare a detailed itinerary, but these places seem interesting: Velebit Mountains, Plitvice Lakes, Zumberak Nature Park, Velika Paklenica Gorge, Krka National Park, Šibenik, Rastoke.
Can anyone familiar with this region give their opinion on whether it would suit my requirements in terms of scenery, weather, and hiking opportunities?
Hey, the Slovenian route you did is amazing, in Croatia you can also find amazing spots, different style to the alps but still great for hiking and sightseeing.
Personally I would recommend: Plitvice Lakes Guide by a Local
Rastoke (Beautiful waterfalls, great stop towards National Park Plitvice Lakes)
Hiking the Tulove Grede on your way down towards Zadar is definitely worth it, also near by you have Zrmanja Canyon. Life on Mars trail on Pag, but there are alot of hikes on Velebit, being our most highest mountain range, you can find most popular routes here: https://planinarenje.hr/gorja , they have a map through which you can pick which would interest you the most depending on your location in Croatia.
I would suggest checking these general tourist questions, they should help you in your planning. Croatia Travel Tips FAQ
Regarding weather, in April you can expect what you are looking for but can really depend at what time you arrive, might be raining, but usually more southern Zadar or Split gets more sunny weather compared to Zagreb but you can easily arrive and have sunny weather for the full duration of your visit.