I really enjoyed season 3.... although that finale was very crazy.... Spoiler The Mad King Dusk ending felt a little too over the top, but I'm still interested to see where Empire goes. Someone else who read the books can correct me, but I believe the face of the Mule was also a ruse and was secretly someone else the entire time.
I really enjoyed it, it was a a great finale. Spoiler To answer your question, in the books Magnifico was the Mule if I remember correctly. In the show they changed it to the social media girl it seems. I would guess next season will pick up right after this season, or a small jump in years, rather than centuries.