Please ignore the 2 green and orange lines in the middle and consider the transistors to be IRF mosfets instead.
First of all looking at the setup on the picture: is there any issues with using 2 completely separate power supplies here one supplying 5V to the Arduino and the other supplying 12V to the RGB led strip (the supplies are not connected on any way)?
Second Question: When using 1 single 20v 10A power supply with 2 buck converters connected to it one of them providing 5V and the other one providing 12V I have noticed the following (without using any Arduinos): if I connected the GND of the 2 buck converters which went to the MOSFETS as well and I used the 5V rail to control the mosfets I could measure 0.5-0.7A flowing through the 5V buck (which would ruin the arduino). Why is this happening? When I disconnected the 2 GNDs, aka the 5V rails gnd and + went into the arduino the 12V rails only to the LED strip I did not see any significant power draw on the 5V rail yet all of these guides recommend you to connect the GND of the 12V and 5V rails in case of using 1 power supply, why?