1) >10. I think what's important is that I like (and in some cases, love) all of these programs, so thankfully I'm not going to be disappointed on match day (unless I don't match...but I'm blocking this outcome from my mind!).
2) I've been sending hand-written notes, sometimes to all my interviewers, but always to the PD and chair. They gave you a few hours of their day, so why not spend a few minutes and write a nice note? Nothing wrong with sending a message of appreciation, email or hand-written. If you have crappy handwriting, I'd suggest sending email.