Magecraft abilities trigger once for each copy created as Show of Confidence’s triggered ability resolves.

The triggered ability counts all instants and sorceries that were cast before it resolves. If you cast instant spells in response to the ability, those spells will count.

If the target of the original Show of Confidence has become an illegal target when that spell is copied, the copies will initially still target the same creature. If you don’t choose new targets for the copies, they each will fail to resolve. Notably, you don’t have to change targets, especially not to opposing creatures, just because the current target of Show of Confidence is illegal.