Thank you so much for your response! I have soldered 100 LEDs, and it works great. Then, it is usable. For anyone who wonders, there is no need to program QMK and stuff, just VIA. Map the backlight keys to any keys you want, and voila. Furthermore, both Cherry and SA do not have any interference with the 2x3x4 LED I'm using right now. Just remember to push the LED down as tight and low as possible.