Create a faction of Greeks? Sounds cool, but it will be difficult to implement.

The Greeks could simply be a style of armor; in Skyrim, the Imperial faction only has the equipment and titles of the Roman Legion – that’s enough.

The Dark Elves have minotaurs and hydras; you could make elf-hoplites, and that’s it.
It’s easier to create Romans because you can use gladiator armor for non-standard units to maintain visual consistency.

For the Greeks, you can make archers and mages in tunics, and infantry in hoplite armor – I think this is the minimum number of units needed (like the Sylvan faction); the rest can be monsters, but I won’t do that – I can’t make tunics, and there are no units in tunics anymore.