I doubt anyone has ever counted but I could be wrong. There are surprisingly few cutscenes (in the original anyway) that feature a lot of NPCs. The opening cutscene has quite a few being a view of the city of Midgar. Maybe the Sapphire Weapon attack in Junon and the Coal Train plowing into North Corel. With the general NPCs that you can interact with around the world: probably upwards of 100. I think newer FF games and maybe RPGs in general have a lot more.
Counting all of the NPCs would be a very ambitious project. I do not personally know of anybody who has counted every NPC per map and then added the NPCs seen in cutscenes to that number. I mean, in some cases it might be hard to determine whether the cutscene NPCs are not the same as the ones that appear on the maps as well.
I would be very interested in learning the answer, though it unfortunately isn't a project I'd have time to pursue myself at this stage.
May I ask what the intention is behind this? Did you want to estimate the population sizes or something?
I wish they'd allow you to pick who to lead the party, even though some can't be "kicked". I know that's not necessarily the point, though.
VII is a great game, and I particularly liked how they reworked Johnny's character in the remake for example. So many good NPCs in the OG that can be fleshed out in the Remake. Definitely looking forward to Bugenhagen.
Ahh... Talking about this makes me want to replay FFVII OG again.
If you truly are planning on doing this, good luck!
Be careful that some NPCs might only be present during very particular moments in the game. For example, standing there saying something before an event triggers but then is never seen again. I'd imagine this would probably require exploring certain towns, etc, multiple times throughout the game.
It would be quite a challenge, I'd wager, though if you were planning on replaying the game anyway then it is doable (watching Let's Plays is also an option, however it would require finding somebody who is actually engaging with the NPCs and checking EVERYWHERE and not just running through the game).
But as somebody who strives to 'comprehend the soul' of Final Fantasy games (myself focusing on the lore and mythological allusions, etc) I can in some way relate to that willpower to dig deep into examining the game like that.