Hi,
Since I am past the hardware part. 
I was wondering how you are doing the software part.
You can set up a thermostat for each room quite easily and open up the valve when heating is required.
But did you add additional logic so your central heating is optimized based on the heating needs of each individual room?
I’m thinking of:
- Turn of central heating when all valves are closed;
- Correct modulation of your gas boiler, each. by sending the biggest different in temperature in a room to the central heating;
- …
I’ve found some inspiration here:
But open to other suggestions.