The books on command aspects are worth looking at - I'm currently reading through Into the Storm.

It helps you put some perspective on how to plan things on a grander scale and has helped me when creating missions using mission editors in various games. You get an idea on what is realistic as far as how many troops should be in XYZ place, and how long it will take for reinforcements or resupply to arrive once certain objectives have been achieved.

They are a bit "lite" in nature, not quite as high detail as I would like but they're a good start. I suppose that the Army Field Manuals would serve a decent purpose for more concrete info.