I always say you should have an Elite/Warrior/Levy split, of something like 3/7/10 for a full stack. Elites are heavy cavalry and elite infantry (including the general and any FMs). Warriors are the more professional fighters, like Neitos, Keltohellenikoi, Milnaht and so on. Also including light cavalry. Levy are your Gaeroas/Gaelaiche, Sotaroas, Iaosatae, and other relatively light, unarmoured infantry to fill out the stack.