Again, the only way a Jojo FPS would work, is going against OP's shitty idea. I want to actually hold onto my idea since it's unqiue, but the best way I'd go about it is make it obviously First Person, but not a full on shooter. There's no reason to restrict one's self to just shooting when the abilities at your disposal like let's say you're playing through each part consecutively, you allow yourself to have so many options that making a somewhat open world with what you have and making it more in line with a semi action RPG not to dissimilar to Zelda more specifically Ocarina of Time/Majora's Mask but more depth, so I guess more in line with Morrowind/Oblivion and I suppose BoTW cause that's honestly in my opinion a pretty damn solid way to go about mixing action RPG with your typical adventure RPGs and shit like Ultima/Wizardry and the like.
I feel like OP just wants to make some shitty Doom II wad where you just have every character have the same shitty gun loadout as it's base for their powers, like let me guess, he probably wanted an ORA ORA gun, a fucking faggot standard punch (or making that the ORA ORA chainsaw/gun bullshit), having stand abilities take up ammunition like a fucking gun (which is retarded) and simply not taking into account how stands are more than just super powers in the sense that they're literally just astral projections if anything, and if lore has anything to say about that, everything would need to be fine tuned where not one character feels the same unless stated otherwise like sharing a handful of similar moves if like Zeppeli and Jonathon shared some Hamon moves, but slight differences or more straightforward, Old Joseph and Young Joseph having the same moves, but visually tweaked or buffed/nerfed accordingly to fit in with the MO. Then for characters that are on horseback like Diego/The World Diego, Funny Valentine, Gyro Zeppeli, Johnny, and even fucking Hol Horse since he road a horse like a couple times, then I believe a motorcycle.
Then for guys with actual guns, that should be easy, but it should just be straight up bang bang shit, you should obviously go back to the comic or manga but honstly I'm so old that I don't even bother trying to act like mangas and comics are some sort of mystical bullshit, a comic is a fucking comic, cept the shit from Japan at least back in the day had a higher standard and didn't look faggy as fuck and didn't get poisoned by kikery like our own homegrown comics did, and at least with Araki he truly tried to be unique and go with something that in Japan at that point in time, was not just fucking strange for your average Jap to bother reading, but almost taboo with the fact you have Ethnic Europeans as the main boys, being muscular, having facial hair and not apparently falling into the typical jap tropes that come with foreigners, and apparently mustaches/facial hair. Which that being said, I truly feel that the Jojo license would need someone who can be eye to eye with Araki and his overall flare. Cause again, the notion of a first person perspective in my eyes can certainly work, but it'd have to be done in such a way where it's overhauled essentially like how Araki did with his own work to where it 'resembles' your average FPS at a quick glance, but is far more out of bounds to where you can merely classify it as an FPS but barely by the skin of it's teeth. I'd go into more depth, but I feel like literally the majority of motherfuckers on here are plebs and are either those disgusting tumblr faggot queers who keep trying to push their cultural marxist agenda in what I would deem a wholesome read/experience that touches on the lines of friendship and tugs on one's heartstrings when you're expecting just kick ass moments and some good social commentary that fits the timeline or is just so balls to the wall it's amusing and promotes thought, or the other half, people who literally just fucking saw the anime and act like they now are little Jojo boyz and how they want to go on kiketube and make shitty videos/watch shitty videos about how "hey guys look did you know that Araki made a SEQUEL TO PART 4?!?! LIKE WHAT THE CUCK!?!", or how they just realized in general that there's a thing called light novels and how that exists, but need to fucking go the autistic reddit kike route of trying to dismantle Jojo with cultural marxist fueled thoughts and research.
It's disgusting when you realize how Jojo is now going down a dark spiral when you start to remember that there are 'fans' just around the corner being the most mentally disturbed individuals on this planet who now cling to Jojo like fucking life support because they're unoriginal, unimaginative retards like dumb faggot children who fawn over sanic making shitty OCs all day, which they do with Jojo as well and it's just laughably bad.