You’re totally correct that Celsius is the more sensible scale with easier to replicate reference points (when using water). It was also invented almost 30 years after the Fahrenheit scale and with all the insights gained from that period of technological advancement. In fact in the modern day the Celsius degree size is defined in reference to the Boltzmann constant since Celsius is essentially the Kelvin scale with the numbers moved around.
It also used 100 as the freezing point of water and 0 as the boiling point when originally proposed, which changed after Anders Celsius died because everyone knew that was a weird way to do it.
As I understand it, yes it was a saturated solution.