2021-06-18 : 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.

2021-06-18 : If a spell with storm has targets, you may choose new targets for any of the copies. You can make different choices for each copy.

2021-06-18 : 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.

2021-06-18 : 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.

2021-06-18 : 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.