Just a quick update:
I've added the code I'm using to control this with (as well as calibrating displays) to my GitHub: Week Teef. It still needs loads of work, as I'm still in the process of figuring things out, but it DOES control the arm with (reasonable) accuracy. I don't know how user friendly the code is yet, I'm kind of flying by the seat of my pants, I will go back and make sure that the code makes sense later; as in I will make sure there are notes everywhere and full instructions. But! If anyone has any questions before then I'd be more than happy to answer them.
Other info: It's written in openFrameworks using Standard Firmata loaded onto my Arduino Uno.
Feel free to let me know if I'm forgetting or missing anything.