Mariah Carey — I’m Rehearsing, I’m Ready, I’m Fabulous

EXCLUSIVE

Mariah Carey is taking her Vegas residency as seriously as anything in her career … so say the people getting her ready for next week’s start.

Our Mariah sources say she will not have a do again of Japan … her voice is “on fire.”  We got this pic of her rehearsing over the weekend with her voice coach, producer and other show-related people.

There’s…