You choose which instant or sorcery card to exile as Torrent Sculptor’s enters-the-battlefield ability resolves. You must exile one if able.

If a player casts a spell that targets multiple permanents their opponent controls with ward, each of those ward abilities will trigger. If that player doesn’t pay for all of them, the spell will be countered.

If you have no cards in hand as Flamethrower Sonata resolves, you won’t be able to discard a card, but you will draw a card. No damage will be dealt.

Flamethrower Sonata goes on the stack without a target. While it is resolving, you discard a card, then draw a card. When you discard an instant or sorcery card this way, the reflexive triggered ability triggers and you pick a target to be dealt damage. This is different from effects that say “If you do . . .” in that players can respond to the triggered ability knowing how much damage will be dealt.