I assume this means that "combat" is not modeled as an explicit event between two players, but rather there is some thread monitoring everyone's assets asking "is this thing being attacked? If so, attack back!" and that is where first strike derives from?

The combat tutorial claims that combat damage is resolved simultaneously to both sides. Does first strike imply that this is not that case and they alternate attacking, or is first strike just the trigger that starts them shooting at each other on the same schedule?