I’ve also built a similar device for experimentation. It uses the MAX30102 to measure heart rate and oxygen saturation. Later, I modified it to directly measure respiration using a BME280 pressure sensor, but it hasn’t been fully debugged yet.
I’ll look into your link as well.
EDIT: I wired a push button to D0 and an LED to D1 instead of a motor, then uploaded the sketch.
I wish there was a “quick start guide” that lets I try things out without reading all the documentation.