Nice guide, everyone should check it through. Few things here definitely I did not know.
It seems a bit retarded that schrecks give immune to cold for Volks, wtf is that shit? Like they are not good enough as it is? (Ok sorry for balance talk but that really is something that makes 0 sense.)
I might add my own tip for control groups:
I usually use CTRL 1 + 2 for my vehicles (tanks) or snipers in early game, CTRL 3 + 4 for my indirect fire (kat, mortars, arti) and 5+ for my AT guns.
Those are easy to learn and in heat of the battle it makes a lot more easier to micro my most important units.