I recently closed a professional production of Legally Blonde, so my insight is tied directly to how we did it.
- Elle had her own dresser, who would assist others when not needed
- A few of Elle's changes were just piece changes (putting a jacket over her Harvard T-Shirt etc) to save time
- Almost all costume changes happened in the wings as opposed to down in the dressing rooms, which technically defines a QC at my theatre, but the actual quick-quick ones for the chorus were Jamaican Me Crazy into Personal Essay, Personal Essay into First Day of Harvard, Bend and Snap into Second Courtroom, and Courtroom/Bathroom into Graduation.
- That being said, we had three non-Elle dedicated dressers, and members of the stage crew would help the chorus with their changes whenever they were able to. Most cases Wardrobe preset everything out and the actors were left to their own devices, and everything went fine. Keeping in mind that your actors may not be used to changing entire outfits in <30 seconds, it may be useful to have some more dressers to assist.
- I have my costume change plot from Legally Blonde; it is all tied to our blocking and costume design, but if you think it may be useful, you may PM me with your email and I'll send it over.