I called and asked how many had to be sent. The lady told me at least 3 but no more than 5, or a committee letter. There is no preference or criteria for what kind of letters to send (clinical vs. science or non-science). Sorry, I don't know where to send them to as the premed advisor from my ugrad school has all of the addresses, I just tell her the schools. I think it is on their site or there is also an address given when you submit your secondary and you get to the payment part. Hope this helped.