That's more or less how I've been playing, except for the number of missile troops. In the west I limit myself to only an absolute maximum of two Greek slingers/archers but in the east it just isn't feasible to limit missile units too much as the Pahlava and Saka (who sometimes come down to Seleukid lands) have so many missile troops, so you really have 3 choices fighting them. Have at least 5 units of archers/slingers is one choice, the second is use spies to avoid open battle and fight a war of sieges and city taking so you never have to face their mobile armies, or third choice is to purposely limit your missile troops and lose every battle.