Adding an Undergraduate Music Degree - STEM kid?

You should be able to handle it. It’ll be a lot of work but your biggest challenge is likely to be Music Theory. Stats and seminar will be what you’re used to and have shown you can handle, and the rest will be “work to do” but not “hard” as long as you stay on top of things.
I’m not sure how the grading goes though, it seems pretty unique to each class/professor.