Worth noting JSS is the default usage in material-ui's component library. Also worth noting, that if you have separate designers, that staying closer to (s)css may be a better option.
It looks like themes are the only way to do this... you can try saving them into your global settings file manually. Been a while since I even considered it.
In general, I tend to favor the mdi packages for icons, it's based on the google icons, but extended with thousands more community based icons.
https://www.npmjs.com/package/@mdi/font
Usually best to write/export a dynamic method that will have a global reference and return the global or dynamically loaded module, assigning the global after loading.
Note: this is expressly for EcmaScript Modules (esm).