Starting a podcast is an awesome idea! To reiterate what the others have said, for a self-driven extracurricular to be Tier C, you do need some sort of quantifiable results. That might mean producing a certain number of episodes (like 50+), getting a certain number of monthly streams (like 1000), or number of 5-star ratings. You'll likely want to learn marketing strategies to help get your podcast "out there," like SEO, networking, and social media. These are also great applicable skills that can give your self-driven extracurricular more weight. Just remember that while there is a strategy behind growing a podcast, be sure to enjoy what you're doing. Colleges can tell if you're doing things just to pad your resume, or if you genuinely like what you do. It can be easy to lose sight of the fun if you're always concerned with stats. Best of luck!
Hello!
This depends on how much tangible impact your podcast has. In order for this EC to be a higher tier, you must have something to show for it ie. it gets written about in a publication like HuffingtonPost or the NYT, or you receive 10,000 streams. Of course, these are only examples but so long as you show that your podcast is recognized and well-established, it will be a substantial boost to your application and an excellent potential essay topic for you to write about.
Hope this helps!
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No problem! The stats help establish it as a higher-tier EC, but it doesn't need outstanding stats to be "legitimate." How dedicated you are to it and how much you develop it will determine its legitimacy. Your stats are not really something you can 100% control anyways, but you can nudge it towards quantifiable success with proper marketing strategies.