Thank you do much for this thorough answer. I certainly wasn't expecting this amount of detail.
I have been looking into ahoeben's (fileofview) Octoprintplugin, especialy how he accesses the PrintMonitor part.
However, since I'm unfamiliar with the inner workings of Cura, it raised a lot more questions, which is why I reverted to not "reusing" Cura's internal features, but just redrawing GUI elements in the MonitorStage and feeding it with values.
Needless to say, that's apparently not the way to go 🙂
@nallath, thank you so much a