Oh, I hope the gay subplot does get more prominence! But yes, the focus should be on Cinderella and her romance.
I know a lot of Cinderella versions and as far as the ones close to the "original' or "real" Cinderella it's pretty much just the original Greecian one, Chinese one, Italian one, and then the ones we know the best, the French one that invented the fairy godmother and glass slipper and the German one which has Cinderella's mother's ghost and the stepsisters cutting their feet. I have never heard the names Sebastian or Marie in any of those versions. However, Douglas Carter Beane's use of "Charlotte" was one of the English translations of a stepsister's name from the French one for the Rodgers + Hammerstein Broadway version.