brimforge said:

So we could have Dooku instead of Sidious, until "Palpatine" reveals himself as "Sith" to Mace Windu ?

No, we just never see Sidious until the end of the series when he's revealed as Palpatine. He is only talked about but has no actual screentime, Dooku controls the federation and the seperatists while he is in search for a new apprentice to help kill Sidious (this makes Maul one if his secret apprentices). This helps build up a reason to have Dooku in the next two movies and also a better explanation for why he is replaced by Anakin