But you only need iron and copper plates to make green circuits; in bigger factories, if you want a central place to make green circuits, you'll end up having to use 3 dedicated belts just for green circuits.

But that's what I had anyway in my last game, a big central line with a lot of the essentials. I think next time I'll go for a central line with just iron and copper and mini bases that take from it, or something. More trains as well, bringing in ore from all over the map.