Ringo Soul Hacking Explained

Seems like Aion developed a technique (that Ringo can use) to hack into the soul of the recently deceased called Soul Hacking (which fits considering the game) and revive them as long as they agree to it in a limbo-like exchange with Ringo.
These individuals get bound to Ringo completely and lose their contracted demons (that switch owner to Ringo instead), but I guess it's better than dying. Curious to see how many characters we get in total playable. Will they be just enough to fill the party or will we have extra character we need to slot in and out depending on situation?