Having read through all this having a new infantry unit could be a good idea.
I know this is my first post but reading through it has helped me think of a way this could be done without over complicating things.
You wouldn't have to build any new facilities as can use the barracks and factory.
Call the unit 'Infantry Support' and say have a max of 20% (random figure could be changed) of your infantry so that not over kill and they give a boost when supplied with munition and other resources aswell (as a possibility) against tanks and Air Crafts these could be used in either Offence or Defence.
Reason for the boost would be that this unit is a combination of Anti-air units, Artillery units, Logistics, Communication, Medical so these would be the background to how armies operate.
