For our company, Belle is doing a more "posh" accent than her normal australian one. The director calls it an international theatre accent. I'm not sure if that means anything to anyone else or he's just making it up.
Babette and Lumiere are both doing strong french accents in their lines and their songs.
Cogsworth and Mrs. Potts are both doing kind of... mild cockney accents.
And Madame (Me!!) is doing the same as Belle.
I don't think it really matters what accent she has really, as long as it's understandable and convincing. I could be way off base though