Yes remember when they invaded Saudi Arabia? That taught everyone an important lesson on the consequences of terrorism on American soil.
Cuba is the easiest target the US could have. It's very close to the US and very far from any potential ally. The US has never shied away from committing acts of extreme cruelty, well into terrorist or war crime territory. From dropping nuclear bombs on civilians, phosphorus bombs, drone bombing innocent people, schools, hospitals, institutionalized torture, etc. even with far weaker reasons.
There is no scenario where a direct attack on the US wouldn't lead to an extremely violent response in complete disregard of Cuban lives. And get away with it.
It seems to have made things better for the Taliban.
We do not know this. There are plentiful evidence to suggest direct involvement of the state itself, and the bin Ladin family is certainly hard to untangle from the Saudi state. That is just from what we can know from unclassified sources.