While I'm not Steve, my personal approach is that a single infantry unit is a squad of infantry (and the transport tonnage or rather, transport volume, includes things like ammunition, weapons, personnel, supplies, tent accommodation etc.) and a vehicle is a singular vehicle including the crew required to operate it as well as fuel, some rudimentary spare parts as well as the stuff for the crew.
As for the formation sizes, I tend to keep individual formations at most at 5kt (or sometimes much smaller) in size to allow flexibility in transporting them and then use them as building blocks to form a proper unit hierarchy. For example in my Red Galaxy playthrough, I'm currently going to have companies of 100 tons (for infantry) or 250 tons (motorized/mechanized), formed into 750 ton battalions (250t HQ), Regiments (2kt HQ + 4 battalions), Brigades (5kt HQ + 4 Regiments) and later into bigger formations as well, in which case I'm consolidating the companies and battalions into single battalion formation layer to lower the micro a tiny bit.