Thank you everyone for your help.
[I tried quoting and nothing happened.]
@ Joakin Agren: I am having problems with various HDDs that are not so old (as opposed to my other machine that is still going strong after over 10 years)… which has resulted in me rearranging the content of the drives… and I have heard that one should not change the orientation of a drive once it has been formatted. [For the record… both the older, good ones and the newer, bad ones are [both] a mix of Toshiba and WD. (I can not bring myself to buy Seagate, after… long story.)]
@ geofelt: I have ended up with an extra motherboard from my last/incumbent build [Z170X-UD5 TH versus Z170X-UD5; vendor just ignored me]… so I have bought a second-hand i5-6600 to go with that. My intent is that, if the motherboard or CPU are bad or fail quickly, everything else should work if I buy a current motherboard and CPU. The point is that I bought a CPU cooler that is (also) compatible with 1200 and 1700 (and AMD) (and I think it was about the cheapest of those). [The TDP for the newer CPUs is much higher than for the 6600.]
@ tennis2, geofelt [and anyone else I might have missed]: Thank you for your advice about the cooler touching the case. It is not this simple, but I guess one decisive element is that I imagined the case wall amplifying some droning sound made by the fan (or the HDDs or the other fans or whatever). I guess I also (subjectively) do not like the idea of ripping bits off my expensive cooler, even if it does not actually matter. (I want a window [e.g. TG] on the side; my personality is that I very much like to be able to see stuff, under such conditions.) I guess in the end I did not want to run the risk of some problem emerging, when I had the whole thing assembled and the case was now “second-hand”. I know the advice has been uniformly that it should be fine, but… I dunno, I’m just too much of a perfectionist, I guess. (I do still appreciate the advice. It is nice to have a clear picture, even if I do end up balking at the hurdle.)
I ended up buying the “be quiet!” Pure Base 600 [orange; the colour is a bit drab compared with the photos] [I erroneously said “Dark Base” earlier], and being annoyed that they do not include as many HDD cages as there are positions. (One can buy extra cages — if one lives in Europe or NZ — but then you could just buy a better case for the same total money.)
Anyway, thanks again everyone.