@joeaddie If you really want high quality and a build that will support whatever you want to do with it, the more important component than even the processor is the motherboard. A B450 board is fine now, but it doesn't support PCIe 4.0, which is just emerging and not really ready for purchase yet but is going to become the standard down the road. That's a few years away, and components aren't fast enough to even take advantage of it yet, plus everything should be backwards-compatible, so it's really not necessary to get a board that has PCIe 4.0 channels now. But if you're looking to have a system that's still overpowered in four years, the faster channels would be worth it.
I didn't include an X570 motherboard because the cheapest ones are an extra £95 and up once you factor in the VAT, and I thought you wanted to keep the budget down. If you're interested though, the Asus Prime is a very good board and should continue to be for the entire life of the computer. Of course, that plus a Ryzen 9 3900 would put you way over your preferred budget, and you'd also want liquid cooling rather than air. (The air cooler is more than good enough for the 3600, but not the 3900 running anywhere near max capacity.) Or you could postpone that upgrade until you have something that offers a real workload to the 3900... it can get kind of complicated.
I priced the same components on another site (PC Specialist), and it came to £1,173, although it's cheaper with a 3800X, but still not cheaper than Cyberpower.
The other option is to not get the stronger processor now, to wait until you have a use for it. The processors you might want should still be available in a few years, and AMD has announced that its 4000-series CPUs, due out towards the end of the year, will work with 500-series AM4 sockets, meaning an X570 board would be fine. From the speculation I've read about the new generation of processor, it should be faster and more efficient than the current gen by a significant margin.
Really though, this is about the choices you're comfortable making at the given price points. I can't tell you the right answer, just the relatively better and worse choices in each category. (For example, do not buy an ASRock motherboard.) There's no wrong approach here.
For the graphics card, I usually tell people that if they're only looking at playing Sims games for the next couple years, get the cheapest card that's good enough for that. GPUs are improving rapidly these days, and performance that would cost you £600 now might be £300 in three years. If you don't know what other games you'll be playing then, or what other graphics processing you might be doing, it's a waste of money to guess and try to futureproof for those theoretical uses. Instead, save the money now, and when you do have another game or other activity in mind, get the best available card for that use at that time.
Overclocking is running a component at higher than its specification. This can be simple or quite complicated. For example, most current motherboards run memory at 2666 MHz or so by default, but if the RAM is faster, you can tell the board to run it faster with a couple of clicks, and this is supported by the board. Many graphics cards are factory overclocked, meaning the manufacturer made the card run at a higher speed than the Nvidia or AMD reference design. This is also supported, and you don't need to do anything to make it happen, the card will just run at the factory overclock. You can also overclock further than that, although there's some randomness to how fast a card can run without having problems.
In contrast, overclocking a processor effects the entire system and shouldn't be done unless you have a good use for it. In fact, other than the memory, I wouldn't overclock any component unless I had a specific purpose, e.g. my GPU was maxed out in a certain game and I wanted to squeeze as much performance out of the card as I could before upgrading in six months. Other people do it more routinely, but that's almost always because they have demanding tasks in mind that would benefit from the extra power. Overclocking also takes a toll on hardware, so no point in wearing it out more quickly unless you're going to replace it anyway.
I know that's a lot of info, but if you're making a big purchase and are interested in learning, there are a lot of details to consider. The nice thing though is that you can get a really good system no matter what choices you make here.
