If a spell has multiple instances of storm, each will trigger separately.

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

Spells cast from zones other than a player's hand and spells that were countered or otherwise failed to resolve are counted by the storm ability.

The copies of instant and sorcery spells you cast created by the storm ability 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.