I avoided a main bus after noticing nearly all the copper went to producing circuits and low density structure, and similarly most iron for steel and green circuits - so just site those close together linked via short buses [1]. Then ship the remaining copper, iron and steel to the Science factory using single wagon trains. (That’s just for a simple one rocket per hour factory)

[1] Cu -> Circuits -> LDS <- Steel <- Fe

I don't this that applies here, since the person I gave the tip to was so overwhelmed that they gave up.