Pretty cool idea actually I like the chintsy decor as well fits well with the theme
Some of your ideas would cause issues as flagged and Im not sure how it would work but I think there is scope to do this
1 x White Female Beta = Marilyn Munroe
1 x Black Female Beta = Bruce Wayne/Batman
1x Black and Red Female Beta = Robin?
2 x Platy - 1 Blue = Spock and 1 Red = Captain Kirk
6 x Pygmy Cories or 6 Otos = Jaws the Great White Shark - closest things I can think of that are sharkish shape and small enough.
Trying to think of something for Alphalpha with like an antenna or long whisker but cant think of anything small enough or that would do well in a low number....
6 ottos would be hard to care for, they ned a good established aqaruim, and they need a constent source of algea, and for 6, that would be really hard to get.
2 platies is alot in a 10 gallon tank with other fish as they produce a lot of waste, if i am not mistaken. the pygmys are great though, same with the bettas