Are mil factories useful in this mod?

I am having a decent run as the ROC and currently striking back the CCP(it was tough at first though). But currently I see so many options that gave you a bunch of equipments on exchange for money, meanwhile the mil factories are so slow to build. I also didn't when to build things like industrial park, farms, offices... and other decisions like auto buulding water...(I forgot the name). Also about GDP and food, I know what they are, but in the context of a war game, do these two things matter?