When it turns into a creature, it is no longer an enchantment.

It changes into a creature even if the spell is countered.

The ability triggers when the spell is cast, so it becomes a creature before the spell resolves.

A noncreature permanent that turns into a creature can attack, and its abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of his or her most recent turn. It doesn't matter how long the permanent has been a creature.