Buy Coy level organizations! If you buy platoons, the HQ unit will have command and rally them all. Coys give you subordinate commanders. First buy, say, Leo2 coy and you will get maybe 7-9 of these (3 platoons). Then click the unit list to remove some of these tank platoons, so you will get the C unit, that is company HQ unit, that commands the now depleted tank company. And FORGET the Leo1A5s! At your experience level in this engine, DO NOT buy them. They have their time and place, but not in your current organization.
Do not negate artillery! Whatever it takes. You will need at least two Leo 2A5 or 2A6 MBTs (Not four). You will not need any Leo1A5s. Trust me on this one.