Never played a Final Fantasy game in my life, except for Mystic Quest through a SNES rom many years ago.
Is it worth playing the 'original' version of VII first (through PSN on the PS5)? Or is it just better to go for the remake and then play this when this comes out?
It depends on your tolerance of dated games, but I would say yes, it is still worth it. Visually it's dated, there's no way around that, with it being the first 3D FF game. But that's only a small part of the experience. Its materia system stands the test of time, as does the world building and especially the soundtrack, which remains brilliant.
I replayed it a couple of years ago and still really enjoyed it, but of course I have the childhood nostalgia that wouldn't apply to you. If you're getting it from the PS Store, you get some QoL changes and modifiers that make getting through it quickly much easier, such as a fast-forward option to speed up any grinding you might want to do.
If you're planning to get into the remake (and rebirth) at some point, I believe just going through the original story once will still enhance that experience, even without the nostalgia.