Literally this mod is Essos Total War, choose one of 21 Essos or Westeros factions, and lead them to domination in Essos, you can play as Volantis, House Targaryen, Ghis factions, Dothraki, all what you want.
Republicans are nonplayable emerging faction, they will appear only if Volantis player or Targaryen player proclaim Valyrian Empire restoration, they have the same units as Volantis, but have no access to Noble Infantry, Fiery Hand(unit will be created for Volantis later) and Piromants.