Glad you've liked it so far!
No, to be honest I didn't even know Rob Zombie made this. I've liked his other films, so I'll try to check it out.
I think there are 57 unique enemy sprites not including palette swaps counting all of the monsters and bosses. Many enemies have 2-4 alt color variations.
For these my plans for naming schemes will differ. For example, Chaneque has three alt palette versions, so I plan on using prefixes like Moon, Sun, and Killer for him and others like him. I really wanted to do del Sol and del Luna as suffixes instead, but that would be way too long with some of the other monsters using this setup.
Others like La Catrina here, will be a little different. La Catrina is a more modern interpretation of the Aztec goddess of death, Mictecacihuatl. So her alt palette will be named Mictecacihuatl instead of (Sun/Moon) La Catrina, since there is an already established different mythological figure.
And thanks for the art offer! I'll definitely hit you up if I get stumped at any point.