I am very impressed with your electrical supply.
Very important note for you, off-the-shelf extension cables could be very risky. I only have two GPU based miners placed in my house. These beasts takes up 1800 watt of input. I have also connected them directly to the electrical grid meter (thats what they call it in India) from where direct electricity can be drawn. I have one breaker in between.
However, over the period of time C13-C14 do not support the heating. I had incidence where my whole extension board burnt to dust. I am not sure how common is tis problem but my experience was horrible.
I have switched to heavy duty wiring now for the room where I have installed miners.
But considering your safety checks, I see myself next to zero in my set up. Lolz.
Hmmm, I hope you're wrong about the extension cables - I have used these in 4 small farms now without issues. The cables in this particular installation have been running constantly since April 2020. They are rated at 10A / 2300W each = 4600W per pair. Deduct 20% for constant load / safety = 3680W per pair, running 3250W load.
The Whatsminers are a different matter though, they pull 3700W at 240v. Initially, I installed 1.5mm cable which did overheat - but later upgraded to 2.5mm cable.