The Character Warehouse is not at Disney Springs; it's off property in Orlando. I think it may be at the outlet malls -- I found this by Google:
There are two warehouse locations in two separate outlet malls in Orlando. One, the original, is located at 4951 International Drive Suite 95 and the other is at 8200 Vineland Ave., Suite 1252. Both carry similar stock, but the location on Vineland is larger.
What exactly is available at the Character Warehouse on any given date will vary. I believe it's like most outlets -- outdated stock, overruns, etc.
If you want a specific look, I suggest going through Etsy. Provide pictures of the accessories you want and see what someone can do for you. As for the hair styles themselves, anybody can up-do your hair - again a picture helps the stylist know what you want.
Costumes are allowed on
DCL during "themed" events -- such a pirate night, Halloween on the High Seas, etc. However as an adult you would not want to be mistaken for a character and guests are forbidden from posing for photos, signing autographs or otherwise "pretending" to be the character. Alternatively you can do "Disney Bounding" which is to dress
similar to a character but not exactly -- for example, a yellow top and matching skirt maybe with rose accents to be Belle. Pinterest has some great suggestions.
Don't expect to have anything available just for asking onboard DCL, even if offering to buy it. If they have an extra supply of sashes it may be possible, but if it's really important to have one you should get it ahead of time (as noted above, try Etsy).
As for Disney Spring BBB location, it's officially listed as "temporarily unavailable" but I honestly would not expect it to re-open.