Interview attire at UCSF is the same as at other med schools - professional attire. Generally, this means a pantsuit or skirtsuit for women, and a business suit for men. I've interviewed with people (at various schools) that wear something different, and it makes them stick out. It's safest to wear a traditional, mostly-conservative suit. Check out the
Women's Interview Attire Thread and
Men's Interview Attire Thread for more advice about what to wear.
Your UCSF interviewers will NOT HAVE READ YOUR FILE. This is different from most other schools. You'll need to explain your "story" from scratch. They will see the rest of your application when they attend the committee meeting to discuss your admissions decision.
Here is the
UCSF Interview Feedback, which contains 100+ entries from former UCSF interviewees. Here, you can see what types of questions were asked of other interviewees. I recommend checking out the interview feedback for each school before you interview.
There are
roughly 10 people per interview day.