All of History, All at Once

The copies are put directly onto the stack. They aren't cast and won't be counted by other spells with storm cast later in the turn.

A copy of a spell can be countered like any other spell, but each copy must be countered individually. Countering a spell with storm won't affect the copies.

The triggered ability that creates the copies can itself be countered by anything that can counter a triggered ability. If it is countered, no copies will be put onto the stack.