And after about 16 not working prototypes made in the past 6 months, I can officially say that this revision of the circuit is the right one, also because it's the only one that worked for 30 min straight without any calibration for about 7 days consecutive. Currently, the frontend can only distinguish between left, center and right position, no blink detection yet.

To fully test the whole project I made a little (and also my first) script in Python to simulate the computer arrow keys and I've played some random driving games on the internet. In the beginning, it was quite strange, but after a while, it felt almost natural. 
The last thing I haven't made was a PCB so, after designing it in Eagle (no KiCad, sorry, it's quite hard to understand for me), and I've purchased a prototype PCB from JLCPCB.

What surprised me about JLCPCB is the price: it's really cheap, I paid 2 dollars without any shipping fee for 5 boards, that's incredible!

I will probably make a video of the frontend working when the PCB arrives, also because will be in the same period when school begins, then I can also show you some cool waveforms on the oscilloscope.