I only buy the tap or die I need. Chances are that it will be the one I’ll use most and it will need replacing again. They are consumables, just like drills.
It gets worse, for a given size and pitch of tap you might need several profiles for specific applications. For example I used to have Taper, First cut, Second cut, Plug cut, for 4BA, 6BA, M4, M3, M2.5 (for my work years ago in electronics). I’ve lost track of how many M3 taps I’ve binned over the years.
I still have the correct taps for helicoil inserts on Vextra, Astra, Cavalier exhaust studs - effectively a non-size that comes with the helicoils. I also still have a bag I bought from an instrument fitter when he retired of maybe a hundred assorted old Imperial (Whit, UNC, UNF, etc) taps and dies suitable for old UK bikes and cars - a fiver in 1973 and I’ve never used any of them but almost unobtainable now!
The most important items is the tool-stock holding the taps and dies. Always have the exact right size both in the jaws and for the way you will be holding it. There is nothing worse than the tap going in off-line and jamming and wrecking the hole, simply because it was sloppy in the jaw or one cannot hold it square to the work. For small threads I prefer a T-bar Tap-wrench where the bar can be locked centrally on the the top of the tee. My M&W trio are really old and I cannot find them for sale now, but one of these ratchet T-bar sets might be useful in confined spaces.
https://www.amazon.co.uk/dp/B01BJ1BSRC/