Spartans... ha-ha-ha... whew, I haven't laughed like that in a long time... read this ( https://ru.wikipedia.org/wiki/%D0%90...80%D1%82%D1%8B ) – it basically describes the Spartan army quite well!
So, don't expect a Greek army from me. I do have an agreement to use models from Greek mods for Mount & Blade, but I don't see a good base for these units. Well, let's say you could repaint an Elven archer to look like he's wearing a toga, but there are no good candidates for infantry and mages, and a slinger would look better than an archer.
I agree that the faction should be good, but, in principle, villains could also work well. Just make the pegasi black, and it would look great! Hoplites in bronze with black cloaks...
But if I were to change a faction within my mod, I'd replace the Forest faction – satyrs and minotaurs would fit well in the forest. In principle, the presence of archers can be justified by saying they are elves, but we'd have to give up on druids – that's a Celtic thing. The Greeks have oracles, which would then also influence the Dark Elves.
Added 3 minutes later
but all of this could change 10 times