Well historically the closest you can get in EUR is 3HI + 1A + 1C where all the historical army regiment types are represented (despite the fact that certainly there were mainly HI and cavalry and archers did not reach 1k each) and you reach the usual 5k men. Unfortunately a legion like that with the game mechanics will not work very effectively in combat. Cavalry is always better to have them in pairs (minimum 2 regiments) as they attack the flanks, and archers are very powerful attacking protected by the first line so it is always good to have them at a number wich is 2 regiments lower than your HI. After some combat testing my legions are of 4 HI + 2 A (same as I originally used on my first game

). I have attachments of 2 cavalry which are independent units and will be used according to need by the basic legions. Having a segmented legion army like this allows you good flexibility colocalising them as needed depending on the opposing army and with very good loyalty balance. Apart from my first game, where I did not know the rules yet, I never had a civil war nor disloyal armies, so everything is very well under control.