You don't have to go with the new ATX 3.0 PSU standard and there are adapters for graphics cards, but it probably makes sense to at this point. 650/700W PSU will be fine if you're not getting a monster graphics card.
So if you're not looking at an ultra top-end build there is plenty of value to be had with an above midrange setup, £600-£1k depending on where you choose to save the pennies. Something like last gen 3070 or current gen 4060 (none of the blower cards).
I would go Intel personally, just because it works best with DDR5 setups, AMD setups with DDR5 are proving to be awkward.
Hardware prices (particularly for NAND chips) are going up rather than down, I would be looking to buy relatively soon before prices go to pot, maybe order the memory/M.2 NVMe now before prices go silly and pick up the rest later.
This is what I bought last year, probably would cost £6/700 now:
GameMax F15 case - very well reviewed and affordable case with excellent cooling
Asus Prime Z690-P DDR5/PCIe 5
Intel Core i5-13600K Raptor Lake
BeQuiet! Pure Rock 2 air cooler
32GB 6000Mhz DDR5 (2x16GB - dual channel is a must)
1TB PCI-E NVMe boot drive
nVidia RTX 3070 8GB graphics card
Since then I've upograded to 64GB DDR5 and swapped out the 650W PSU it came with for a 1kW Platinum+ I purchased ages ago on sale, there was nothing wrong the 650W really though. The i5 with all those cores feels face-melting compared to my 10 year old rig, can't see why you would need to spend more on a CPU unless going nuts for benchmarks and 4K ultra gaming.
Oh and if you really don't care about graphics performance drop in something a little older even, like a 1660 Ultra for £100, it will still play all your games
