The second question was answered succinctly by Mohd,

So I’ll start on the first answer; I’m sure Adam DiAngelo provided a very good design for the whole network—opening it up for the huge growth it’s experienced—but a lot of the credit for Quora’s greatness goes to ‘the writers who supply its content’ (and of-course to the sponsors who pay for it, and the administrator(s), who—along with many others—can confirm or deny the exact details of this mostly-guessing response).