Hi, I was wondering if you had any guidance towards post-processing Fourier Output

How did you derive the below formula utilized here?
Math.pow(10, 5 + wave[i] / 10)

I checked the blog, by the way, super helpful and easy to read blog.
and it said:
but we can improve data for analysis by using Math.pow function

there's a 'highest' string but no 'hightest'.

Regardless, a better term would be "thinnest" and "thickest" so it doesn't get the confusion people have over the metaphor of "high sound" vs string-closest-to-the-ceiling. Otherwise, "first string" is the standard guitar term.

So you don't need to keep up with lives

I suggest AGPL as this is a web app. But anything compatible is acceptable enough, see http://www.choosealicense.org if you're not sure about license issues.