I love the choice for Cheetah to be in the film as she's Wonder Woman's most iconic foe. I'm a big fan of the Female Furies but I would save them for Justice League 2 or the New Gods film. Plus they're really not specifically Wonder Woman enemies, so that would be odd.
Kristen Wiig is a great actress and we haven't really seen her do something like this role, so I'm hesitantly excited and optimistic she will pull through. I don't think she was on anybody's list for Cheetah castings, but I think she'll fit the Barbara Ann version very well.
I don't think the movie version beheading Medusa would sit well with movie-going audiences, though, especially since many interpretations of the myths have her as a sympathetic figure. Sure, she killed Ares in the first film but she also spared a monster like Doctor Poison.
I'm pretty sure the fact that her rogues gallery is predominantly female has something to do with it. Many writers just don't seem to want to use female villains (unless they're of the femme fatale variety, which most of Diana's aren't).