How many extracurriculars should I participate in if I am hoping to get into a top 20 school?

Answered

The Common App has 10 slots that you can add activities to, so the short answer is 10. Now remember, the word "activity" is used VERY broadly here, so those 10 can include clubs, sports, musical ensembles, internships, summer programs, volunteer work, jobs or employment, etc. Publishing multiple pieces of writing would fit under one of them as well. For most of the students I've worked with, you're way more likely to have to narrow down your overall list to 10 and leave some things out than you are to struggle to reach 10. (And truthfully I would aim for a higher number, as long as you can handle the workload, to give yourself options on what to pick.)

What I would focus on, since you've already reached a pretty significant level of involvement as a freshman, is picking a couple of activities you want to develop further and gaining some leadership experience through them. They don't have to be connected to medicine, but they could be. In any case, colleges like Brown want to see significant involvement and responsibility taken on by the students they admit; they want to know that you're able to handle running an organization, or managing a team of people, or spearheading an initiative or program, because those things tend to translate well as indicators of success down the line.

And since you mentioned the spike—I've said this a lot in answers over the past week (because suddenly everyone is asking about it), but I think the language around it obscures what's really important there. Ivies are looking for students who have demonstrated that they a) have a unique talent or skill that they've worked to hone or b) deeply care about something and have taken steps to put that passion into practice in some way. The "spike" is not about the actual accomplishments that people tend to cite (e.g., you absolutely do not need to have published a full-length book or started a national organization or released a functioning app to get into an Ivy), but more about having a passion that comes through cohesively on your application, and that you've used the resources available to you to pursue—with bonus points if it's interdisciplinary or particularly unique, or connects to your goals for study.

So an interesting question for you might be, how can you combine your skills with writing and English with your interest in studying medicine? Could you start a blog or newsletter that advises people your age on how to deal with medical questions or common medical issues? Could you pursue medicine from a journalistic or reporting angle? (That's particularly relevant right now—there really has never been a better example than the COVID pandemic of how important competent science writing and medical journalism is.). Heck, write a medical thriller novel and then write one of your essays about the experience of drafting it. You have a LOT of options here that would all work well, and would give you an interesting and unique profile from most other students aiming to pursue medicine.