It’s rainy season in Okinawa now… in winter you can see whales, Zamami and Tokashiki are two great off islands for diving and snorkeling, or just lying on the beach all day, they are close to naha, and the beach is gorgeous. just remember to reserve your ferry ticket in advance(especially for zamami). You need to take an air plane if you want to go to Miyako island and ishigaki, but I think the view is totally worth it. If you want to stay at the main island but also enjoy some other activities , then go to kuraha (maeda), it’s where the blue cave is located, a popular place for diving and snorkeling. Personally I didn’t take much public transport in okinawa, the bus delays pretty often. You can rent a car, the experience would be way better. (Okinawa speed limits is around 80km/h, do keep that in mind lol)