@axel I had the same thought as well, but awhile back I came to the best decision for me (and I can't stress that enough because what I'm good with may not vibe with you at all):
I'm getting this now, ASAP, and if there IS a PS5 version for Part 1, I'll bite the bullet on that too.
I came to this conclusion for two reasons:
1.) Since the original is my favorite game of all time, I don't mind having multiple copies, DEPENDENT on what a PS5 version has.
2.) IF the PS5 does backwards compatibility Series X is doing (where it's somehow automatically uprezzing the previous generation's games in the hardware itself), then having the PS4 version is fine for me. HOWEVER, I don't think Sony is doing the same thing in that area, or if they are not to the extent, quite like Xbox, so I would much rather experience this as soon as possible.
Again, that's just me, and your criteria is for you to help you determine what's best for you.