Personally I would always have a separate OS drive. Makes it easier to reinstall windows and stops clutter/maintains boot speed.
Edit: 2 others beat me to it. I must go on a typing course.
You could ring PCS but I doubt they will know. The cards are basically all the same so paying the extra £100 depends on whether you are prepared to wait or not. It could be days or it could be weeks, especially as it's the Chinese holidays at the moment.
There are ways to upgrade if you google it. It requires registry hacks and could be overridden by Microsoft at any point in the future. I managed to upgrade a 10 year old laptop with no TPM and an unsupported CPU.
You can upgrade to Windows 11 if you know what you are doing. It needs a few registry tweaks and a pen drive. I did a 10 year old laptop and it works but runs like a dog lol. Not recommending it, just saying it is possible.
No, you are not understanding how it works. Ubuysa explained it very clearly. The CPU is designed to run at 100% (or sometimes more) so it is not "stressed" as you say.
If you are that concerned then limit the number of threads the zip utility uses to less than 24, I suggest you google how to do...
It isn't how much CPU it uses, it's how long it takes that matters. If it used 1 core it might take 12 minutes but using all 12 cores would take 1 minute. Bit simplified but you get the idea.
There seems to be a mix up between VRAM and system RAM in this thread. It is a surprise though that system RAM of 32GB is dropping relative to 16GB. This will have less effect on gaming than VRAM.