Maul was a wasted opportunity, in my opinion. Either use him as the PT's villain as whole, building him up and up and up (killing Jedi, like Qui-Gon and Sifo-Dias and the like) until he faces down Anakin, showing Anakin's skill and fall to the Dark Side in order to defeat Maul.
I don't mind Dooku as the face of the Separatist movement, especially if he appears in Ep. 1 as a Jedi Council member, who retires after Qui-Gon's death (as the EU states). Bring him in as the elder statesman who tries to force the Republic's hand, before Maul leads the war (instead of Grievous).
As for Kylo Ren, I'm really hoping he has an active role in TFA. Hopefully Snoke remains a more mysterious character, like the Emperor in ESB, and is expanded upon later.
Also, too many villains in TFA? Um, there are not any more than ROTJ of even ESB? You have the crime lord on Jakku, Kylo, General Hux and Snoke. There is not that many who can't all work together.