What kind of concert is it? If it's a classical concert, lighting will be much easier to deal with as opposed to a full rock/metal concert that is likely to have a full light show.
I wouldn't really lock exposure when the spotlight is on the performer and keep it there for the entire show, it'll black out the rest of the stage and performers. It depends on the lighting conditions, if it's a rock concert there will be wildly different lighting conditions throughout the stage.
My personal approach would be to lock aperture (I would shoot wide open, usually) on the main performer(s), lock ISO on the max you're prepared to go, and then micro-adjust shutter speed throughout the night. Anticipate bright moments and not-so-bright moments as you go. Keep the camera on manual settings because if you don't, the camera is going to fluctuate wildly trying to over- or under-compensate for the wild lighting conditions (if it's a rock concert).
An incandescent setting might not be best white balance setting, I don't know what kind of concert it is but there may be all kinds of lighting going on throughout the show. Shoot raw and post-process later.