How to control ceiling fan speed with ESP8266 + PCF8574 (using normal regulator type control)?

[newuserimscit]

Hello everyone,
I’ve been working on a home automation project using ESP8266 (NodeMCU) and PCF8574 I/O expanders connected to relays.
So far, I have successfully managed to control multiple lights/bulbs dynamically – I can control 4 × PCF8574 modules = 32 I/Os (manual switch as well as the corresponding light/bulb control works fine).
Now I want to extend this to control a ceiling fan with speed regulation.
In India, ceiling fans are usually controlled using a normal step-type regulator (capacitor-based). My requirement is:
Fan ON/OFF should be controlled through a relay (like the lights).
Fan speed control should be possible (preferably replacing or emulating the normal regulator).
Integration should still be possible with ESP8266 + PCF8574 (as my current setup is based on that).
My questions:
What is the best way to interface a ceiling fan regulator with NodeMCU?
Can a PCF8574 + relays setup handle this, or do I need a special fan speed controller module (like triac-based dimmer circuits)?
Has anyone implemented fan speed control (not just ON/OFF) in such a setup?
Any guidance, circuits, or reference projects would be really helpful.
Thanks in advance!