@Jas, a few thoughts/comments - feel free to take them onboard or not 
I live the Wemos D1 Mini and it’s expansion possibilities. However, like all ESP8266 based MCVUs it has a limited number of GPIO pins. When you start adding more relays, motion sensors etc then you may run out of appropriate pins.
See this for more info…
The simple solution is to add more D1 Minis, which would mean using Blynk bridge to communicate between them. This is do-able, but can be a challenge.
Or, you could move to an ESP32 instead.
One way to do motion sensors is to use 433MHz PIR detectors that are battery operated. Each detector will transmit a unique code when it detects movement, so you could have a 433MHz receiver attached to a D1 Mini or ESP32 to receive and process these movement signals. This has the advantage of allowing autonomous battery operated PIR sensors to be placed in convenient locations, and having your control unit tucked away in an appropriate location next to your HVAC system.
My preference for a control system like this is to use Node-Red as the heart of the system, and use this to interface with Blynk, google assistant, amazon alexa, external weather services etc etc.
Communication to/from the MCUs is then done via MQTT messages, which gives a robust platform that can be expanded easily in future.
I also like to use Nextion touch screen displays rather than the little oled ones, as they are much nicer looking and quite easy to use.
More on my climate control system, built using this architecture, is here:
Since I wrote this I’ve had some new aircon inverter units installed that can be operated by an app as well as an IR remote, and the next thing on my list is to sniff the HTTP protocols used by these and establish a 2-way control/feedback system for them, but that’s a little way in the future yet.
Pete.