Everyone here is in a constant battle over 1-page vs 2-page resumes. Whatever, I don't want to get into that, other than to say that the schools I applied to would specify if the max was one page or two.
But do put it on two pieces of paper if it's more than one page. It's more professional and the interviewer can look over the whole thing in a glance, instead of having to flip back and forth.
Definitely add updates, and even point them out to the interviewer. Do try to be smooth about the update, slipping it into the "walk me through your resume" question. The interviewer may make note so that the adcom knows about it too.