Its up to you to decide the size of the legions in EB, make it a 'house rule'. In the second Punic war the Roman senate raised six legions, which is quite impossible in EB to achieve, the best I can get is to raise a full Consular legion in 4 turns, thats a year in EB. If it helps you here are my house rules for the legions.
A Legion is composed of 3 Maniples of Hastati and Principe, two of Triari, 2 units velites, one Accensi and a cavalry ala, I use the Romani Equites.
A Consular army is bigger in size, we know that it was double the size of a standard legion, and that the Allies where equal or more than the Romans, so here how I solved the problem. Either raise the number of maniples of the above to 5,5,3, or add two maniples of Hastati Samnitici and two units of Samniti Milites, and take 3 manples of Triari. To them add 2 other units of Velites. That will raise the number of units to 17, the 3 free slots can be filled with cavalry. Two ale,Roman cavalry ( I am against using them against other cavalry, they are only good to pursuit), Campanian or the Extraordinarii. Don't forget the consul. Generally I take 3 characters, a Consul and two Legati, thats more fun.
I also like to substitute one Milites Samnitici unit with the Pedites Extraordinari, and when possible take a unit or two of Lucanian infantry. These lads are of great support to your cavalry against other cavalry.
Cheers.
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