i have gone for a 1 on 1 ratio :P a full stack legion of mine contains about 4400 men. (1200 velites, 1200 hastati, 1200 principes, 720 triari, 100 cavalry + the general). The romans usually had the cavalry attached to the allied legions until the imperial times when they had the 900 alae. So for now every legion is supported with a full stack allied legion of differing sizes and make up.