Well... I still have a raid6 on this PC and for this kind of capacity, spinning disks are a must.
SSD for my boot disks are still enough while they still work and 256gb are ok (for me, because they're JUST for boot a a couple things more). SSD's are also cheaper than M.2, still and I don't need the M2 performance, not to mention, you don't get much more than 2 slot which, when pressed for space, might not be enough.
For reference, the torrents for FP and VP posted in this site, amount to 1TB. That's before you extract anything, of course.
But my curated folder of extracted tables for FP and VPX (I only play VPX tables), amount to 23GB and this includes tables and backglass files.
My VPX and FP install folders which are separated from tables folders, amount to 16GB mostly because altsounds, altcolor and roms folders for VPX.
The puppacks install folder that has the puppack stuff, is already at 6gb...
So, yeah, I still prefer the spin disks for storage as it is cheaper and I can wait a few seconds more to load a table :D
In the end, it's how you'll use the space.