To me, “no interest in a STEM major” pretty much says “do not apply to MIT”. However, I think that the advice from the MIT “applying sideways” blog is also accurate for other selective universities, including Brown. As I understand it, the recommendation is that you do what is right for you, and do it very well. This basic approach has worked well for my family, but what each of us has done has been very different (and this approach has taken us to very different universities).
If Calculus with Applications is the right class for you, then take Calculus with Applications.
I was a math major. I always liked the applications of math. If you don’t have a use for it, what is the point? I lucked out in that I took regular calculus at the same time as calculus-based physics, and the professors were obviously in cahoots. We got to use much of what we learned in calculus a few days later in physics. Seeing how it is useful helps a lot when studying math (which again suggests that calculus with applications makes sense).
And this is also very true.
Similarly, I would not “stock up on APs” for the sake of university admissions. Instead, take the classes that are right for you. Keep in mind that during your senior year of high school you will also be very busy with university applications, visiting schools, deciding where to attend, and related activities.