"Strangely, with no real evidence, I don't think the Party wants a war--at least not this soon, not yet. If the communists thought for a moment that the US and Japan would stand down while they invaded Taiwan, they would begin immediately."
Agreed with your speculation. Here is my speculation: Taiwan is the little ploy to start a big war. The real play is the Middle East. We could stop them just like Japan in WWII in the Pacific and the Chinese know this.
However, we get involved in Taiwan and China uses this as an excuse to attack our "allies" namely Kuwait and Saudi Arabia. Their army could roll right through the Middle East and if they cut our supply of oil off, their would be nothing we could do to stop them, pending using nukes on them.
I tend to think that, to the Chinese, Taiwan is an end of itself, although an invasion of the island might have a broader aim. Who can know with any certainty what the Chinese intend? Such an assault would certainly have a global ripple. Any opponent would want to disrupt our economy as much as possible, and oil is a notorious Achilles heel for the US. I disagree, however, that the Chinese would find a Middle Eastern adventure the stroll through the park you describe. It is easier to sink tankers to disrupt our oil supply than it is to send ground forces rampaging through thousands of miles of hostile desert.