I think 2-3 is good advice, as long as those 2-3 are strong extracurriculars. Meaning not a 1 day or even a 1-week project. Admissions committees will want to see that you didn’t do the EC “just to put it on your resume” and is something you dedicated some time and passion too. For some examples and my personal advice for a medical school application – check out the post “The Four Pillars of a Successful Medical Schoool Application”