Let's Control It

I need to build a silencer box for a projector, which will have 4 PC fans (12V), same speed (parallel wiring?), so no individual control needed.

I assume they’ll need to run at full speed, but just in case: If I want to have the option to control the speed (based on the temperature inside the silencer) using an ESP8266 Wemos D1 mini and ESPEasy, which type of fans do I choose? 3-pin or 4-pin PWM? I mean can the PWM signal of those 12V fans be attached directly to the ESP8266? Or do I need e.g. L298N motor driver board anyway?

Main difference between 3 and 4 pins is that the 4 pin variant allows to control the speed by sending a PWM signal to the fan.
The 3-pin variant only allows to count the pulses from the fan.
Since you need to control several fans, the return signal of all fans has to be counted separately as each fan may have a slightly different rotation speed, or run slightly out of phase with the others.
This means you cannot mix the fan tacho signal as the final signal may be somewhere between the minimal and 4x the max. tacho pulses.

I think the simplest way is to use 4 pin versions as the PWM signal from the ESP may be fed to all fans.
You may want to use a transistor as I do expect the PWM voltage level may need to be higher than the ESP may deliver.
Then you can simply use the "pwm" command to control the speed of the fans.

Thank you!