QIf multiple other Dragoncraft followers that cost 3 play points or less are put onto my field at the same time, does this follower's ability trigger once for each of them?

AYes, it does.

QIf I have 2 copies of this follower on my field when another Dragoncraft follower that costs 3 play points or less is put onto my field, do the abilities of both copies trigger?

AYes, they do.

QIf I can't select an enemy follower on the field when another Dragoncraft follower that costs 3 play points or less it put onto my field, can I still deal 1 damage to an enemy leader?

ANo. If you can't select an enemy follower, you can't play this follower's ability.