Play around with it in single-player. I think if your opponent doesn't contest you for gardens (As you knew he wasn't doing here, since he opened Envoy), it's optimal to gain something like 5 ironworks before your first gardens? This obviously differs if your opponent contests you for gardens.
Remember, ironworks are non-terminal, they don't collide. If you draw multiples in hand, use the first bunch to gain more actions (more IW, or villages, or crossroads) and then the last ones for green.
Also, the trade route is not helpful. You don't want trashing here. It looks like it gives you +buy, but that's a lie, you trash one card for the +buy, so it's like getting nothing at all. If you'd opened ironworks/crossroads or ironworks/silver, they would have worked better. You ended up trashing a few estates to it - coincidentally, if those estates hadn't been trashed, you would have ended up ahead on points.