How fast can you actually type on it before the game UI can’t keep up? Are you keeping some kind of input buffer to deal with that?

Yep, it uses an input buffer. I ran some tests it seems to max out around 45wpm. If you type faster than that, the characters will still be added to the buffer and get processed, but you’ll eventually have to sit and wait for the movements to play out (at about 45wpm). For reference, my best rate unassisted (using a standard GameCube controller) was about 20wpm.

I just finished the video, that was incredible! Great job. I subscribed