I have two concerns about the code:
You can run a running average in the arduino code, instead analog reading 4 times per second, you maybe read more times per second avoiding the noisy read. https://www.arduino.cc/en/tutorial/smoothing
Even though the Steinhard equation have a well known constants, its recommended run the equation in the post processing (with excel, python, etc), instead in the arduino code. Why? If you have a bug in the code will lose precision trying recover the "correct data" or in the worst case escenario you will need rerun the test.
After that, nice analysis and really good plots.