I started collecting Superman villains month issues, and so far I got:

• Cyborg Superman, both 3D Lenticular and standard cover;
• General Zod, 3D + standard;
• Metallo, 3D + standard;
• Lex Luthor, 3D + standard

and I plan on getting Parasyte 3D + standard and Brainiac 3D + standard, and are Doomsday and Darkseid also Superman villains, 'cause Doomsday is a Superman/Batman title and Darkseid is a Justice League villain? And are there also any other Superman villains in the Villains month?

There was Bizaro and H'el as well. And yes, technically Doomsday is a Superman villain. I beleive it got relegated to the Batman/Superman title because his two solo titles already were taken basically. As for Darkseid... It's debatable. He traditionally appears as a villain for Superman, although he was created in the New Gods titles originally. But he does also feature as a JL villain too. I personally count him among Superman's rogues gallery though