>>717752648 (OP)
If you just wanna check it out, probably just play 7.
If you want to get into it, play 4, 5, and maybe Zero, then 7.
(I say "maybe Zero" because 7 has direct callbacks to 4 and 5 that you'll appreciate if you've played them first, but not to Zero).
If you really want to get into it, do the above, but also definitely play Zero and play the fan translation of 3. Then go from there with the other entries. The first two are underrated.