QDo I resolve this follower's "Whenever an Aqua Force follower on your field attacks" ability before an opponent can play cards and abilities with Quick?

AYes. When attacking, all abilities that are triggered must be resolved before non-active players can play cards and abilities with Quick.

QIf I have 2 copies of this follower on my field, do I give my leader +4 defense and draw 2 cards the 3rd time an Aqua Force follower on my field attacks each turn?

AYes, you do.

QIf an Aqua Force follower on my field attacks but is destroyed by a Quick card or ability, does its attack count towards the condition of this follower's Strike ability?

AYes, it does.