Control a light with a potentiomter (via MQTT)

Configuration
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Hello HA community!

My question is about, how to control a Philips Hue bulp with a hardware switch and a hardware potentiometer.
The hardware switch should switch the lights on/off and the hardware potentiometer should control HUE, SAT and BRT.

On HA side I found the Philips Hue bulb in Settings > Devices & Services > Entities (entity.ID: “light.f”).

There directly and as well with an additonal switch on the dashboard I can control this bulp for on/off, brightness, colour temperature, etc. .
No issues.

On ESP8266 side I have a hardware switch and a hardware potentiometer.
The MQTT client (running on a Wemos D1 mini) publishes following values:

mqttClient.publish("/Bathroom/Light/HUE", String(PotiHUE).c_str());  //Example value: 110
mqttClient.publish("/Bathroom/Light/SAT", String(PotiSAT).c_str());  //Example value: 150
mqttClient.publish("/Bathroom/Light/BRT", String(PotiBRT).c_str());  //Example value: 180
.
if...
mqttClient.publish("/Bathroom/Light/Upper", "OFF");   
if...
mqttClient.publish("/Bathroom/Light/Upper", "ON");

With the mosquitto of HA I receive the published topics and the values.
No issues.

I checked this HA documentation for “MQTT Lights”…

… and attached following code to my configuration.yaml:

#--- MQTT ---
mqtt:
  light:
    - name: "Bathroom Light"
      unique_id: 'LED674'
      state_topic: "/Bathroom/Light/Upper"
      command_topic: "/Bathroom/Light/Upper"
      brightness_state_topic: "/Bathroom/Light/BRT"
      brightness_command_topic: "/Bathroom/Light/BRT"
      rgb_state_topic: "/Bathroom/Light/HUE"
      rgb_command_topic: "/Bathroom/Light/HUE"
      state_value_template: "{{ value_json.state }}"
      brightness_value_template: "{{ value_json.brightness }}"
      rgb_value_template: "{{ value_json.rgb | join(',') }}"
      qos: 0
      payload_on: "ON"
      payload_off: "OFF"
      optimistic: false

In Setting > Devices & Services > Entities I find now this new entity “Bathroom Light” (entity.ID “light.b_light”).
With the hardware switch attached to the ESP8266 I can now “Bathroom Light” turn on and turn off.

So far so good.

My 1st issue is:
I can’t control the brightness and I can’t control the color temperature of “Bathroom Light” with the hardware potentiometer attached to the ESP8266.
Is this a topic of converting string in integer or something like that?

The 2nd issues is:
How do I connect “Bathroom Light” to the real Phlipps Hue bulp (entity.ID: “light.f”)?
I think I need some additional code to link both together, may be via the entity.ID?

I found some similar questions from other about this, but unfortunately I can’t bring this together to solve my issues.

Many thanks in advance!