Why would the Chinese need to take Okinawa first if the Miyako Islands are closer to China? Is it because Taiwan would protect them?
The distance between Okinawa and the Miyako Islands is just 150 miles, close enough by FAR to guarantee a costly air/sea battle with Japan.
Were China to take the Miyakos (totally uncontested Japanese territory and home to maybe 40,000 Japanese and featuring a 7,000 foot airport, quite easy for an Il-76, etc) they would almost certainly have to take Okinawa at the same time, in order to thwart an easily mounted counter-attack from there.
Of course, that would involve the USA.