Number 20 right now is @utopian-io with 53,964M approval, or 13.59% of the total upvotes, according to steemd.com. The exact number is 53,963,817,252,985,466 on @utopian-io's account page.
According to @penguinpablo's last report (https://steemit.com/steem/@penguinpablo/weekly-report-how-much-steem-is-stored-on-the-exchanges-september-21-2018) there is 49,020,275 STEEM stored in exchanges, out of a total of 80,334,683 liquid STEEM and a STEEM supply of 277,168,974.
Now, I believe the approval weight = VESTS, and looking at the stats at SteemDB seems to bear that out, although it is confusing because they are currently two weeks out of date.. My VESTS is listed as 152,674 and my vote weight is 152,674.
So, let's assume that 53,964 M approval (ignoring all those extraneous digits) = 53,964 MVests.. We also have about 2020 VESTS = 1 STEEM, or 495 STEEM = 1 MVest. That means we need about 26,700,000 STEEM to vote somebody into the top 20. (That's at least a plausible number. It can't be 26.7 billion and it shouldn't be 26.7 thousand.)
There is currently enough STEEM in the exchanges for you to acquire that much, though at the current price of about $0.86 I don't think it's feasible (and certainly would move the market significantly.)
You might be able to lease some of the necessary SP instead of buying it.
No, the amount of Steem you have, is not synonymous with becoming a top witness.
Witness are voted into the top 20 by accounts on the Steem blockchain. Members with accounts on the blockchain vote in accordance to what the witness has to offer to the community, and monetary worth is at the bottom of that checklist, if even present at all.
It would take so much Steem to game that system, that everyone would know what you're doing, and the other 19 tops (and entire community) would have no respect for you, whatsoever.
You can buy your way into the top 20 witness spot but you can solicit your way into the top spot by coming out with a proeject that would benefit many steemians having high SP and ask for their witness vote in return. That's what most of the top 20 witnesses did. If your project benefit steemians and they see that you have the interest of steemit at heart, they would vote for you.
No. you also have to compete against teh mega account @freedom who pretty much makes you a top 20 witness if you have his vote because it is so large.
No. To get in the top 20 you have to pretty much have the huge vote from the accounts of @freedom and @pumkin and they are both owned my Ned from my understanding.