The sequels have already been named and plots revealed...
...They are...
Nosferatu-Too (about Nosferatu's unknown son)
Nosferatu-3: Foe (about a huge lifelong Foe of Nosferatu)
Nosferatu-4: 6-6-6 (Nosferatu tries to go back home, to Hell, but instead "finds himself" along the way; sort of a coming-of-age road comedy.)