Yeah taking some of the Ryukyus to build airbases and host anti ship missile forces would probably be an early objective to support the blockade. Depending on how bad the US is hit in the initial stages it wouldn’t even be out of the question to see an amphibious operation against Okinawa.

China would basically need to invade Japan to cut off Taiwan, ensuring that the USA and Japan are involved very early, so that makes an up front amphibious operation more likely.