That is very impossible to know. That is the reason why it is an anonymous way of making transactions. No one's name is attached to any public address unless they display it and that is the only way you can even know the amount that has probably gone through it via blocktrail or blockchain which still doesn't guarantee the amount they have.

All the above, except for exchanges and some who bought in early which may have a whole lot, we can't still say specifically even though I have seen some rich list in the past.

Also, no one knows if satoshi actually had such an amount of coin as that was just a speculation but I would not be surprised anyway. Who wouldn't have? I am sure it would even be more than.