Does Astral Heron count itself?

Yes, it counts itself. You play Astral Heron as your first card of the turn. After it resolves and is finalized on the battlefield, its triggered ability evaluates the condition — it sees that you've played your first card and that Astral Heron is now at a battlefield, so the trigger fires. When that trigger resolves, your next card (the second card you play that turn) costs [2][A][A] less.

So you play one card (Astral Heron) to get the discount on the next card. It does not discount itself.