Thanks for commenting. I don't have all the answers to the questions you pose here, there definitely was a high number of accounts - please see my post today - I think there were circa 155 designated mining accounts, and there is 300k of STEEM still in those accounts....
https://steemit.com/ocd/@cryptocurator/are-these-steemit-inc-ninja-accounts-is-there-an-unfrozen-whale