原文Iron Fist's ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered or otherwise leaves the stack without resolving.
原文Casting multiple spells that target a creature you control in the same turn will result in Iron Fist having multiple instances of the activated ability. You can activate only one of them at a time, and as this will require tapping Iron Fist, having that ability multiple times doesn't accomplish much.