Running extra logic along with ESPEasy firmware

[billymac]

I need some tips on how to proceed with a project I am working on
I am a big fan of ESPEasy and for the most part have been able to get it to work for me.
So far I have only turned some relays on and also created rules successfully that turn the relay on by pressing a button and turning the relay off after a timeout.
(without requiring internet connection)
I want to add some custom code to do some more specific things and do not want all the logic to live in Node-red
Like with the relay timer I mentioned I would prefer to have the logic on the device in case of an internet issue.

At this point I am unsure how to proceed since there are many options.
So my main question is can I add custom code to the esp on top of the EspEasy firmware or would I need to add my code to the firmware files and re-flash it or could I just add it as files like you would do with Node-MCU/LUA and include or call the code in those files.
Or maybe I can do it all with rules and/or dummy devices
To give you an example of the type of things I want to do...
Based on a particular MQTT topic being received...
- run some code to simulate a led candle flickering
- control an LED setting brightness and color

If this cant be done easily I would consider creating the code for the device(s) from scratch probably using Node-MCU on the device but my preference is to use Visual Studio so I would look into using Visual Micro (better than Arduino IDE) but for that I don't know if I need to flash the original AT firmware or use Node-MCU/LUA firmware.
... Or maybe I can use Visual Micro along with ESPEasy and do both at the same time- that would be nice...