Ok so, its definitely been a while since I last updated this, but never fear! I've been getting so much done lately. I might also reiterate stuff I said in the last post. The FFT works really well, and I was able to code a method in arduino that turns the stepper motor in response to whatever the FFT is spitting out compared to the desired frequency. Here are my results after a bit of tweaking  (ignore the 440hz, im using a free trial of an app): 

As you can see, the tuner was able to get each string relatively close to what it was supposed to sound like. It works the worst with A since the code has trouble accurately detecting frequencies in that higher range.

After getting the code to work satisfactorily, I decided to start working on the actual product as a whole, and making look like something nice instead of a bunch of wires. I also decided to work on creating an interface, so that people with literally 0 coding or tech experience could use it. This was very hard for me as I am really bad at CAD, but so far, it is looking really nice. Now, I'm figuring out how to get the entire circuit to fit into this cute box!