light-v

To be fair if I were to choose I'd rather watercool the GPU which is typically noisier and hotter than the CPU when gaming
Same applies to CPUs yet AIO liquid cooling is very popular

Keyboard and mice can be extremely personal it's very hard to recommend something on the basis that it's a popular product. 
 
With that being said you can check out Rocket Jump Ninja's top mice list. He is one of the most well known mouse reviewer out there :
https://www.rocketjumpninja.com/top-mice
 
Keyboards are even harder to recommend due to the many flavors they come in so I'd suggest you order from a retailer with a flexible return policy and try a few until you find something you like. 

If you are in the UK I'd suggest going for the HE-400i 2020 as you won't have to deal with customs and having retailers here means you've got warranty coverage (Hifiman occasionally have QC issues, I naver had any but that's something to keep in kind) than if you were to buy the HE-4XX. Do bear in mind as @Psittacpointed out they are not the same headphones but the differences are very subtle though
 
Regarding hissing I'll still suggest trying first before pulling the trigger on an external source, planars are less sensitive (requires more power to draw than typical consumer audio) and therefore are less prone to hiss. 

Your best option is the Schiit Fulla 3 at $99 and you won't even have to upgrade from it with the HE-4XX/400i

You will need to check your motherboard's manual which contains a diagram with the pins where you are supposed to plug your power button. 
 
I don't think I need to explain why your PC won't turn on if you don't plug the button

After that sentence, I suggest you to watch a guide on how to build a computer. You obviously don't know how and tried to wing it and failed.
Here is one from LTT.
https://youtu.be/v7MYOpFONCU

This is a bit vague, can you describe what happens when you press the power button? If nothing happens have you checked the wiring of the power button? 

One thing to note is that windows will cache program files in ram, so you might not even be testing disk io, but cpu speed and how fast it can read from ram. 

I have a 250gb 600p for bootup.
 
and a tiered raid 0 in storage spaces with a sun f40 and 4x 2tb hdds. Fairly fast, all old parts. Just steam games so I don't care about losing it.
 
For the nas I got proxmox and zfs. raid 1 for boot drives, raid 50(kinda) of 4 and 8tb hdds for data, and a 8 drive raid zero for vms using sun f40 drives. one of those sun f40 drives is used as swap aswell.
 
For the colocated server, I got ssds in raid 1 for vms, raid 5 of hdds for storage, and a raid 1 of the 16gb optane m.2s for boot.
 
I think I got some weird setups.

It's no noisier than any of my case fans. To be fair, I have a Thermaltake Suppressor F31 case, so noise is a little less of an issue overall. Given that it's free, it's pretty decent.
 
Edit: Watch this - 
(and see the comments)

I am not sure about what you mean. Are you afraid that a SATA SSD will bottleneck an nvme one? That's not how it works though 

Coil whine can occur without being an indication that something is going to die. Many components emit coil whine and it is completely normal.

You're not wrong.  I don't know if he feels that his videos are family friendly, but the cursing (even if censored) and lewd humor suggest he's catering to adults.  Marking your videos as 17+ on YouTube is probably a good way to kill your channel, which is probably why he doesn't do it.  

Having said that, he uses Doom because it's a new game and it's very well made: you get great results with great graphics, and the game is playable with almost any hardware, making it a useful control to compare that hardware.  If something better comes along, he may retire it, but given how often he plays Tomb Raider despite that game being practically ancient by video game standards, it might be around for a while.  

Because DOOM > "gentler" games.

Any reason not to install your radiator at the front of the case? It'll barely affect case temps if you have it there and will give you better clearance above the motherboard

It's a combination of supply limitations due to the pandemic, scalpers and people skipping the 20 series and are itching for an upgrade. Also demand for anything gaming is insane not just for graphics cards, monitors and top gaming mice are pretty difficult to find too
 
Edit: there is still the used market if that's an option

Supply is super low right now. I checked all the big ones: Scan, Overclockers, ebuyer, Novatech, Aria, Box, Amazon all out of stock. Your best bet it waiting for supply get better or spamming F5 on all of them unfortunately 

You speakers are probably not powered and take their power from the cable so even if you made the connection wireless you would need batteries for each individual speaker.
 
Lets say you find a way to power the speakers and then have some wireless connection instead of a wire, who says that every individual wireless connection will have the same latency, your speakers will not be in sync.
 
Its a complicated endeavor.  Its not that hard to hide the wires

For the S2 I'd add them to the top. The front and bottom are too restricted and probably won't add much. For example. the thermals in my S340 elite don't improve at all when adding 2 fans at the front because of the solid front panel. Try experimenting to see what works best for noise/thermals you might not need the extra fans after all. Is your CPU/GPU temps hitting the 80/90s ? if they're cruising at 70 you're perfectly fine 

Your GPU is most definitely gonna be the bottleneck at 4K, in fact the difference between Zen 1 and Zen 3 at 4K are minimal even 1440p is a significant bottleneck 
 
Have a look for yourself:
 
 

Cooling issues caused by extra fans are way overblown. The biggest factor with cooling is mostly noise rather than performance. Most modern cases handle cooling reasonably well even "hot" cases like the H510 as long as you don't run an overclocked RTX 3090 
 
You won't notice the difference even in the worst case scenario with the S2 unless you are physically covering all the vents. 
 
The biggest downside of adding more fans is extra noise unless your run them at low RPM but then again this may neglect the benefits of adding more fans to begin with.
 
Not really unless you like physically big cases and you plan on adding custom watercooling. 

No.

I bet you've done some research on this one already but yeah it's a pretty popular one on r/Monitors it's a great monitor for the price. I just recently moved to 1440p myself it's awesome

Could be someone spoofing your number. Don't give any info and report to your local authorities if you suspect any scam

Could be someone spoofing your number. Don't give any info and report to your local authorities if you suspect any scam