Okinawa Buses and Sites

I will be visiting Okinawa in January, but I have a few questions about the sites and travel on the island:

1. Which castle ruins are truly worth visiting? Shuri Castle (not in ruins) is on my list, but what about the others?

2. I do not drive and am not skilled enough to ride a bike in the street, so I will be heavily dependent on the bus. Is it possible to go from Naha to Nakagusuku, and then to Zakimi all in one day, with enough time to visit each castle ruin?

3. Same as above, except Shuri Castle to Nago City (possibly for the cherry blossom festival) and then on to Nakijin?

4. With changes to the historical record of the tragedies of Okinawa during WWII, are the museums in southern Okinawa still worth visiting?

5. I'm interested in scuba diving in Miyako. Are there any diving outfits with guides who speak English?

Thanks

Which castle ruins are truly worth visiting? Shuri Castle (not in ruins) is on my list, but what about the others?

There are some ruins around Shuri Castle, although the main palace buildings are recent reconstructions. It is by far the most interesting castle site, in my opinion.

Second on my personal list are the ruins of Nakagusuku Castle:
http://www.japan-guide.com/e/e7107.html

And third comes Nakijin Castle:
http://www.japan-guide.com/e/e7110.html

But I have not been to Zakimi.

As for bus transportation, it is probably possible, but it needs lot of research time of bus timetables and the bus network:
http://www.rosenbus.com/

With changes to the historical record of the tragedies of Okinawa during WWII, are the museums in southern Okinawa still worth visiting?

Changes to historical records? Are you referring to the recent efforts by the central government to whitewash the role of the military in history textbooks? I don't think that the exhibits at the museum are affected by it. In any case, a visit is highly recommended if you have the time:
http://www.japan-guide.com/e/e7105.html

As always, thanks for the great help. And yes, regarding the government's white-washing of the whole WWII history.

There is a museum at the Heiwakinen Peace Memorial that describes the "Typhoon of Steel" and doesn't pull any punches. I think many people visit the memorial but skip the museum. Also, a new Prefectural Museum is under construction but maybe will be open by January, in Shintoshin (Naha).

I'm not a diver but there are certainly English-speaking dive shops on Okinawa and I would be very surprised if some on Miyako did not also, at least enouigh to make you comfortable.

When you visit Shuri Castle, let me suggest three other places very nearby that are free or nearly so: 1)Kinjo Stone Steps, which will take you to 2) Kinjo Dam (small museum there for dam enthusiasts), from where you can walk to 3) Shikina-en Royal Gardens (closed Weds.), my favorite place in Naha!

Thanks Steve. I already planned on Shikinaen and the Peace Memorial Museum, but I knew nothing about Kinjo Steps and the Kinjo Dam. I will definitely put these 2 on my itinerary.

The steps are historic (rebuilt recently of course, and the dam is new. They are not spectacular places, just low-key. They give a small flavor of Okinawa, which is why I like them. It makes a nice walk from Shurijo to Shikinaen via the steps and dam. Another personal recommendation - if you are interested in traditional arts or fabric art, there are a few bingata workshops in Shuri that are open to the public.