Have to say with my background individual room control and measurement always seemed the nirvana, but it seems like a lot of heating design is moving away from this to more constant input / constant loss with outside temperature curve adjustment. Take a look at heat geeks.

You’ve got quite a complicated system there. Some of the key design parameters are about getting balanced flow (proportional) rather than bang bang controllers so that you optimise the delta flow return and operate the heat source at lowest realistic flow return values for efficiency.