I agree with you. I am not new to custom work on PCs and etc. But when it comes to electrical stuff - I will higher a professional. I am in the US. I know a couple of solid US companies that make custom cables to length. I would have them make the cables to the lengths and let them do it. I promise I will not be my error if something faults like that. Way too much $$$$ on the line for this one.Do what I do is draw on the paper with the wiring diagram of each pin with voltages and colours. As the colors on come cables comes in black might be tricky to know which one does what but the standard atx is the same across the PSU board this is where the digital multimeter (DMM) can be useful to make sure the connections are made. And to custom make the cable shorten or lenghten can be achieved by cutting, soldering and heat shrinks and sleeving the overall cables involving using crimping the pins to the plugs this may not be available to buy depending where it located. So to be honest it a lot more work to achieve tidy cable management. Including measuring the cables and visualizing where everything should go before it even started. As it looks simple on videos but a lot more goes beyond this
Right now, I am trying to see when that motherboard is coming out and at what price. This motherboard is brand new, and just posted today. I looked at Asrock just yesterday and never saw this. So now I have to be patient and I will start getting some parts!