what Faction restrictions are there?

[Florence]

I'm looking for more information on how restrictive factions are. I know that you can only join a guild/clan that's the same faction as you. How about partying in the open world? What about chat? Is it like WoW where we can't party with the other faction or speak/whisper to them at all? Or is some communication or partying possible?

 

Finally, is the faction choice ever reversible? My friends are split on which factions they joined so if we can't communicate/party and it's not possible for us to change factions once chosen at level 4 or so, that's going to really be a problem for me.