I have decided to use sensors and actuators based on ESP8266 SoC from ESPRESSIF. They're available in many shapes and configurations.

I use the D1 Mini boards (which are sold under various names): D1 Mini NodeMCU, 

The module has:

• dual power input 5V / 3.3V
• Micro USB input for power and programming
• WiFi 802.11bgn module (yes, "only" 2.4GHz)
• several digital I/O pins
• one analog input with 10bit ADC
• is programmable via Arduino IDE after importing the right libraries

For the start I was "lazy" and after evaluation I've found out, that most of the expected tasks could be performed by flashing and using alternative opensource firmware project: Tasmota

Tasmota supports many modules based on ESP8266 including the Sonoff devices (small compact modules with relay). And huge amount of sensors. 

For me the best benefit is, that the primary communication mode of Tasmota is via MQTT messages via WiFi.