Having given it more thought, I’d expand the saga to twelve films — three main trilogies & three standalone films preceeding/bridging the trilogies.

Episode I: Prologue (Obi-Wan/Anakin origin)
Episode II: Clone Wars I
Episode III: Clone Wars II
Episode IV: Clone Wars III
Episode V: Interlude I (Purge)
Episode VI: Star Wars I
Episode VII: Star Wars II
Episode VIII: Star Wars III
Episode IX: Interlude II (Thrawn)
Episode X: Sequel I
Episode XI: Sequel II
Episode XII: Sequel III