I don't think China would open the invasion with a surprise attack on the main island. I think they would attack the many small islands, owned by Taiwan, located in the surrounding seas. The most important of these are the Pearl Islands, or Penghu. The Qing conquering these islands - they're located a ways off of the heavily populated western coast of Taiwan - lead to the immediate surrender of the Taiwanese Ming rump state ages ago. The most easy to conquer of all the islands would be Quemoy, which is within spitting distance of Mainland China. Once all the islands were within their control, they could militarize them as they have other small islets in the South China Sea. Once they had these bases in place, they could threaten a blockade the of main island backed up by an expanded net of missile defenses, which seems to be their MO when it comes to expanding their security umbrella. Taiwan is very food insecure, much moreso than the Mainland, and couldn't long survive any kind of blockade. The US Navy would probably take pretty high losses if they ventured into the overlapping missile defenses. It might end as it did the first time that the Mainland expanded into Taiwan all those years ago: with the other side seeing the writing on the wall.