So for your scenario I'd personally be looking more into a centralised control system. For an off the shelf solution, something like Tekmar's product offerings (Made in Kelowna!).
I'd start with their Model 400 boiler/4 zone house controller:
https://www.watts.com/products/hvac-...ntrols/400/400
Add a Model 323 4 zone expander
https://www.watts.com/products/hvac-...ntrols/313/313
Add 5x Model 532 Tekmarnet 2-Wire Thermostats (allows you to reuse the existing wiring in your wall)
https://www.watts.com/products/hvac-...ostats/532/532
Add Model 486 Gateway for IP connection
https://www.watts.com/products/hvac-...sories/486/486
Not going to be cheap, probably looking at a couple grand all in, but you'd get superior control of your system than any other "smart thermostat" solution out there. Like the ability to do water temperature scheduling based on outside air temp (IE if it's warmer outside the system will reduce water temps accordingly, saving you energy)
Just FYI hvac control/building automation is what I do for a living, albeit on a much greater scale (IE institutional buildings etc) with much more complex systems.