Yes that number has been mentioned before.  Here is one example: https://forums.butterflylabs.com/bfl-forum-miscellaneous/1736-tour-bfl-offices.html#post23453

Your second question.. that's another key thing.  It's what we were guessing here (full post on my blog like below):

http://mineshaft.me/wp-content/uploads/2013/04/hashrateperbox.jpg

Multiply each guess by the number of units and you have total hash rate.