Cable management can be frustrating but is also not essential. I've patiently worked out what goes where so I can group it and route it. Other times I've just gone with the birds nest method and shoved it behind the PSU and hoped the wires behind the motherboard panel won't prevent me putting the back panel back on the case. Get yourself some small cable ties, they work wonders and are generally easy enough to clip off if you make a mistake.
@JoyKyller like
@TheJudge said it is not essential.
The main thing to keep in mind is that the cables are easily accessible in the event of failure or upgrades / swap outs.
I can recommend getting a strip of velcro (something like this
Takealot ) and cut to length. Higher end PSU's and cases come with this sometimes (eg: Fractal) It will make your life a lot easier with the build. Also most half decent cases that have the PSU at the bottom also have a shroud / cover whcih will also help hide the un used cables if you are not going for a modular PSU.
My general 2 cents worth, from my experience over the years, choose your board and case first as this will determine what you can support out of the box (eg, how many NVME's you can run, PCI-E version for your GPU and of course which CPU you can run or upgrade to)
Small things that are overlooked on the motherboard such as VRM heat sinks and such can also affect what kind of cooling you can run (for example a large air cooler might not fit on a board with larger than normal VRM heat sinks)
I would personally choose the power supply last after selecting everything else to make sure you gets something that can sufficiently run what you have and allow for upgrades in the future (don't cheap out on a PSU. Buy a well rated brand with higher wattage now rather than have to replace the PSU coz its sh*t unit and cant take a slightly larger GPU in future - you can use outervision to calculate a good metric for what to use here
Power Supply Calculator - PSU Calculator | OuterVision )
Other than that good luck with the build and have fun with it