The firmware supports up to 8 external sensors of different types. Keep in mind that the chip has limited performance. You cannot attach 8 sensors, 4 inputs, UART, and get a good result. Some sensors cannot co-exist with each other.
You may add most external sensors on input or output pins. It does not matter. If a sensor has additional options like an address, I recommend adding it to an output pin. Otherwise, the firmware will use the default options for the added sensor.
Common Zigbee information for all external information:
Zigbee cluster: ZCL_CLUSTER_ID_GEN_ANALOG_INPUT_BASIC
ATTRID_IOV_BASIC_PRESENT_VALUE - the sensor value (single-precision float).
ATTRID_IOV_BASIC_DESCRIPTION - the value units (V - voltage, C - temperature, % - humidity, m - altitude, ppm - air quality, CO2, TVOC).
Zigbee commands: read, write (for some sensors)