I get bigger the more you take away from me

A word I know, six letters it contains, remove one letter and twelve remains. What is it?

My first three letters are an upside My last five letters are a unit of measure Somewhere within lies everywhere, everyone, and everything Now sound them all out together and you get...

Try your luck as you throw me down, I move quite well for not being round. My magic number is twenty-one, just try not to lose all your funds.

My first three letters trick and deceive, my last four letters make music you weave. A cloistered soul wedged in between, altogether I’m a puzzle unseen. What am I?