The Free Greek City States are made up of various cities spread out across the map....Massilia, Syracuse, Dalmatia, Crete, Corinth, Athens, Boiotia, Bithynia, Chersonesus, Bosporan, Western Cyrenaica, Rhodes, etc. Each of these cities is a 'mini-faction' in it's own right...most of them have a very diverse unit roster that is better than RTW's original ones, and are unique to them alone. The reason it will be a hard campaign is because you'll be able to recruit NOTHING outside of those cities. So you might call it the 'AOR Campaign from Hell'.

Originally, it wasn't going to be a playable faction...but popular demand made it so. And, you need conquer only 40 regions to win, so it won't be THAT hard.
As far as recruiting Spartans, only the Free Greeks can do that. No one else. The reasons for that are many...model sharing and our future plans for swap factions. RS2, Sparta and the Free Greeks are all set up for the swap faction process as far as recruitment goes, and Sparta is the faction that gets swapped out.