I imagine the settings for each plugin are stored in some json file somewhere? If so, where would I find the settings file for each plugin?
typically plugin settings are stored in config.yaml along with OctoPrint's settings. Plugin developers can choose to store those settings elsewhere, which typically is under the basedir (/home/pi/.octoprint/data on octopi image).
I just got to that section in the plugin Hello World tutorial - figured it was the config.yaml! Thanks for confirming!