You should ignore the impact, if any, that this might have for university admissions. Instead, do what is right for the activity.
However, you might want to keep in mind that in a couple of years you will be going off to university, and you might not have any time at all for this particular activity. Figuring out how the activity would best be served to continue after you are gone is a valid thing to think about.
This sounds like a very good start. If it turns out that turning this into a 501c3 is the right thing, then it is not like you started the activity from scratch. It is more like you helped the activity to grow and mature.
Do the right thing. Treat people fairly. Keep your grades up. Apply to a variety of universities including at least one and preferably two solid safeties. Keep your budget in mind. This will work out one way or another.