Hi,
there much less in use as there tend to be no Optical drives anymore and even storage if in the form of a NVMe drive connects direct to the motherboard with no cabling. so your right its much less a thing. a SATA cable for a SSD drive if you have one but often they come with a motherboard so I wouldnt go out and buy any. Fans may come with the case but if not yes you may need those also. Depending on the CPU you might need a CPU cooler - AMD comes with one, Intel often do not, depends.
The 2 big issues for you at the moment are
1. Very low stock on CPU and Video Cards - there been a load of new tech out since October and for various reasons there all like hens teeth so the prices have gone up if you can even get one at all of most Good CPU and GPUs.
2. GPU (or video cards) are really really expensive now with like £600-£800 kind of money, And"cheap" gaming ones which used to be £150 dont exist anymore so brace yourself for 300+ prices at the very least. To help you need to decide what resolution your gaming so if you are running a 1080p monitor then its much less power needed, if you move to 1440p, your having to spend a bit more and for 4K gaming its top wack for everything really GPU wise.
Any idea on the CPU your going for yet ?