"2. Persians conquered Greece--- in my story the large number of Greeks moved to friendly barbarian tribes, or to their colonies. The northern Greeks would form the Greco-Germania empires. Any other possibilities?"

Seems more likely to me that the Greeks would have stayed where they were, like the other urban cultures (Phoenicia, Egypt) that were conquered by Persia. I do not recall any massive exodus of Greeks from Ionia when that was conquered by Persia.