Therefore, you should be careful in giving this key. It should not be used actually. It should be kept confidentially. Keep your Owner key in an offline storage (Not connected to the internet).

The owner key is actually not visible via steemit.com, so doing the steps above is probably not possible for most of the steem users. What you probably want to say: Keep your master password safe, never use it to log into steemit.com, put it offline.

Owner key is like you Master Password, that key gives you full control of everything.

The master password is actually used to derive all keys from a single password, including the owner key. See the entry paragraphs here or steem.center wiki

Are you sure that the master key can decrypt memos? I don't think so.

I believe our Memo Key is also needed when we send SBD or Steem from Poloniex to our Steemit account.

NOOOOOOOOOOO!

Never ever use any Steem key, not even the public ones, on exchanges or webpages other than steemit.com or steemconnect.com!!!!!!!
Don’t use steem keys as transfer memos! Analysis of private & public keys in transfer memos and implications to encrypted memos