it depends on the types of music they sing. Susan Boyle singing S&M is beyond my imagination

Nope, there's a lot of heavy set people who are very successful in the industry. There's also a lot of skinny beautiful artists that flop, so body image has nothing to do with success.

No

When she first hit it big, she was a toothpick.

Beauty can help a female artist become twitter/paparazzi popular, but that doesn't always translate to record sales. Male artists don't have to rely on looks or sex to sell as much except when they're really young.

I think yes.
It def can help while being fat not that much.