English Usages

Hi,
I have some questions. I have read some entertainment news, and I am not sure if they are grammatically correct.

Katharine McPhee was a runner-up in American Idol in 2006 and has gone on onto a successful pop career, if her $130,000 Aston Martin V8 Vantage roadster is anything to go by.

Don't we say," has gone onto something?"

Next, I heard people say," that is all to it." Is it a correct usage? Does it mean," that is all it is?"
And to in the case is a prepostion? Could you give me some examples?

Thanks,