does heron count as the first card itself when played to a bf

Yes — if Heron is played to a battlefield as your first card of the turn, it triggers on itself.

The trigger checks the game state after the card's play completes, not before (Rule 419.4.a). So when Heron finishes resolving and is sitting at a battlefield you control, it "sees" its own play and fires — the discount then applies to the next card you play after that trigger resolves, not to Heron itself (FAQ #12236).

Two conditions matter: it must actually be your first card that turn, and it must enter at a battlefield (not your Base). Play it to Base and it won't trigger off its own play, since the "if I'm at a battlefield" clause fails (FAQ #11906).