I was thinking of something along the same lines for Delphi (besides the mercenaries, which would be the Phocaean version of chosen hoplites). Ideally, there would be a building which would give a huge one-off monetary boost when destroyed, to simulate the ransacking of the oracle's accumulated offerings, but since the AI doesn't destroy buildings (unless we script it somehow) we can make a building similar to Corinth's diolkos.
I believe Thessaly should have the potential of becoming a hegemonic power (with Jason of Pheres in mind) - even though it minded its own business historically. Still, eight provinces seem a bit much now that I think about it...
About Athens and Corinth, there could be two more factions to represent their islands (pushing the total number of factions to the limit), but I'd place their development importance secondary to fleshing out the other new factions.
Here's a banner I've made for Phocis (based on Phocaean coins of that period):
And one for Macedonia:
I like the idea of black for Phocis and royal blue for Macedonia. The colours of the other factions are less crystallized. As for symbols, I've been thinking: bull's head for Euboia, horse (or horse's head) for Thessaly, Chimaira for Akarnania, either boar or combination of spear point and boarjaw for Aetolia, possibly a grape for Locris, and I haven't done any proper research on Epirus yet.