such a cool idea! I would love to see an expanded mission tree, perhaps you could consider adding some missions about choosing whether to focus on the cavalry or infantry and add a unique unit "companion infantry/cavalry" depending on the player's choice

Adding to that previous comment, make the Seleucids a light blue like in Imperator Rome and be able to restore Hellenic religion.

make it a formable, and make it to be able to choose coptic or zoroastrian