The good news is your kiting life is about to drastically improve. Okinawa has two seasons: summer and kite season. Summer is no wind or light southerly winds, big puffy clouds, hot, and rediculous humidity. You are probably familiar with that by now. About the last week of September or early October you will go to bed and wake up and the weather will feel different. The wind will be out of the N-NW and it will be comfortable. It is now kite season, and for the most part the wind will stay out of the N until about March. It really happens like someone threw a switch. You should be able to ride around 3-4 times a week. When the switch turns off around March it is not as dramatic, and just start to get fewer rideable days and lighter winds. Now learn the quickest route from Torri across the island to Kai Chu Doro. You can read about it on the link posted. Oki actually has a pretty big kiting community, and you will see that when you get there. I was there about 4 years ago, and there was about 40-50 dedicated riders and you would have days with 20+ people out. Kai Chu Doro is one of the few places with a sandy launch and sandy bottom. So it is one of the safest, easiest places to ride. However, you still always want to ride in booties. Okinawa coral and lava will rip you up if you step or walk on it. Also Oki has huge tide changes. If you are new to kiting make sure you go at lower tides. At low tide there is a huge sandbar (100yds) that you can launch from. At high tide it is a very small beach and makes launching difficult. It is not the prettiest place to ride because it is inside a bay/lagoon and it is not the crystal clear water like other places in Oki. However, the wind is usually perfect side one also making it an ideal launch.
There are some other really cool places to ride, but none as user friendly. Most of the launches are pocket beaches and can have a lot of obstacles: fish traps, trees, rocky beaches, lava/coral, and other kite wrecking things. I wish I could go back because I am much more comfortable with my wave riding and I think there are a few places you can ride waves. There is not many and do not remember meeting anyone who did ride in the waves. I have windsurfed a few ok wave spots. If you are into exploring there is something I wanted to do and never got to do it. Google Tsuken Island. South of Kai Chu off the east coast. You can take a ferry over there and the beaches look very exposed to the predominant wind. Clear blue water and large sandy beaches. Never met anyone who kited over there, but it looks like it has serious possibilities, and just a cool place.
My quiver when I was there was a 13M and 10M. I probably road them about equal percentage. However, I wish that I had brought an 8 also. Over the winter I could have road about 20 days on a smaller kite. Around Christmas I remember it blowing over 30 for about 8 days straight. You probably can use a spring suit into December and a 3/2 until about end of February. As mentioned you can also some times squeak a few sessions in as a typhoon approaches and stays offshore. If you really want to ride during the summer (April - Sept) then you need a big kite (14-16) and a light wind board. I spent those months Spear fishing and traveling around, and then waiting on Typhoons for wind and waves. If you surf there is surf on Oki, but there are two types: crap or world class. Most of the time it is crap. Surf is extremely fickle and then when it comes it is super hollow perfect reef breaks.
Okinawa is an awesome place. The people are wonderful, food is great, water is beautiful, and the kiting is good (for half the year).