1) trolling planes attack at the expiration of the 15 minute countdown timer.
2) To split a stack, click on split and move the sliders to create the stack that you want and move them to another location.
3) A country can still have troops without having any provinces. When they lose all their provinces. they lose all their resources, so it becomes very difficult for them to produce more armies. They would have to capture a province, have the necessary buildings, get the necessary resources and hold the province long enough to produce a new army.