Incidentally, here's all the names I will/would use for Part III Stands manifested through Stand By Me and the musical stuff that inspires them. Credit where it's due, the vast majority of these were thought up by people on the internet in threads asking this exact question.
Anubis: Black Blade – The name comes from the Blue Öyster Cult song "Black Blade" in the album
Cultösaurus Erectus, and is a reference to Stormbringer, the malevolent living sword of the Elric Saga of fantasy novels written by Michael Moorcock (which I'm a big fan of, incidentally).
Atum: The Game – The name comes from the Motörhead song "The Game" in the album
Hammered. The song was written by WWE music composer Jim Johnston as the entrance theme for Triple H and was performed live by Motorhead themselves in two of his WrestleMania appearances.
Bastet: High Voltage – The name comes from the Electric Six song "Danger! High Voltage" in the album
Fire.
Dark Blue Moon: Ocean Man – The name comes from The Ween's song "Ocean Man" in the album
The Mollusk. You might recognize it from an old commercial for the Honda Civic, or the end credits of the
Spongebob Squarepants movie.
Death 13: The Reaper – The name comes from the Blue Oyster Cult song "(Don't Fear) The Reaper" in the album
Agents of Fortune.
Ebony Devil: Voodoo Child – The name comes from the Jimi Hendrix Experience's song "Voodoo Child" in the album
Electric Ladyland. It's one of Hendrix's most famous songs, and as is often the case with him, the guitar and vocals are mostly improvised.
Emperor: Big Iron – The name comes from the Marty Robbins song "Big Iron" in the album
Gunfighter Ballads and Trail Songs. The song tells the story of an Arizona Ranger's duel with an outlaw named Texas Red; Robbins got the idea and the name from a one-off custom handgun chambered in .45 Colt with a cut down 9 ½" Marlin rifle barrel that he saw in Andy Anderson's North Hollywood gun shop sometime in the late '50s.
Empress: Offspring – Named after the American punk rock band The Offspring.
Geb: Aquarius – The name comes from the album
Aquarius by R&B artist Tinashe. This album was her debut as a solo artist after the disbanding of The Stunners.
Hanged Man: Centerfold – The names from The J. Geils Band song "Centerfold" in the album
Freeze Frame. The song is about a man feeling conflicted at the sight of his old high school crush appearing as a centerfold in a dirty magazine.
Hermit Purple: Deep Purple – Named after the English rock band Deep Purple.
Hierophant Green: Green River – The name comes from Creedence Clearwater Revival's song "Green River" and the album of the same name it appears in. John Fogerty used a name he used for a river near where he lived as a child that he called Green River even though that wasn't its real name (specifically, it was Putah Creek in California).
High Priestess: Substitute – The name comes from The Who's song "Substitute," which was released as a single before appearing on the compilation album
Meaty Beaty Big and Bouncy.
Horus: Snowblind – The name could refer to several songs named "Snowblind" (all three of which use the title to reference cocaine addiction, incidentally), but I prefer the one by Black Sabbath (though I totally recommend the one by Steppenwolf) from their album
Vol. 4.
Judgment: Magic Man – The name refers to the song "Magic Man" by Heart, from their album
Dreamboat Annie.
Justice: Thriller – The name comes from Michael Jackson's song "Thriller" and the album of the same name it appears in. Obviously.
Khnum: Who Do You Want to Be – The name comes from Oingo Boingo's song "Who Do You Want to Be" in the album
Good for Your Soul.
Lovers: Time Out of Mind – The name comes from Steely Dan's song "Time Out of Mind" from the album
Gaucho.
Magician's Red: Fire on High – The name comes from the Electric Light Orchestra (ELO) song "Fire on High" in the album
Face the Music. I was seriously tempted to use "Disco Inferno," but that was just too corny. I also considered "Fire of Unknown Origin," but…
Osiris: The Gambler – The name comes from a Kenny Rogers song called "The Gambler" in an album with the same name. The song is probably the origin of the "know when to hold'em, know when to fold'em" saying, or at least it popularized it.
Sethan: Forever Young – No, not the Jay-Z song, which is actually titled "Young Forever" and is a reworking of the song "Forever Young" by Alphaville. I hate that song because my mother played into the damn
ground for months after it came out. Instead it's a reference to the oft-covered song "Forever Young" by Bob Dylan, from his album
Planet Waves.
Silver Chariot: Quicksilver – Named after the American psychedelic rock band Quicksilver Messenger Service, sometimes credited as just Quicksilver.
Star Platinum: I've actually got two ideas for this one. The first is "Starman," the famous David Bowie song that was originally released as a single before being added to
The Rise and Fall of Ziggy Stardust and the Spiders from Mars. I'm actually leaning more toward the second one right now, though: Mike Oldfield released an album called
Platinum, which begins with a four-part composition of the same name, the last part of which is called "North Star." "Star" and "Platinum?" I can't be positive that it's where Araki got the name, but it's cool either way, and hey, "North Star" makes for some obvious
Fist of the North Star jokes. And honestly, I might just keep Star Platinum's name, since it sort of counts as a musical reference already, just a more subtle one than usual.
Strength: Meddle – The name comes from the Pink Floyd album
Meddle. The name references how its powers are usually used; "meddling" with the ship to hurt and kill people. I'd have used an explicitly boat-themed name, but that was kind of too corny.
The Fool: Mr. Sandman – The name comes from the old song "Mr. Sandman," originally written by Pat Ballard and recorded by too many artists to bother naming; the most famous today, thanks to pop culture, is the version recorded by The Chordettes. I considered "Enter Sandman," but I like including one or two older songs every now and then.
The Sun: Here Comes the Sun – The name comes from the Beatles song "Here Comes the Sun" in the album
Abbey Road. George Harrison wrote it based on his relief at the arrival of spring and the concurrent break he got from dealing with the band's business affairs.
The World: Could it be anything but the album and song recorded by Ronnie James Dio himself? No, surely the only name worthy of Za Warudo is [Holy Diver]! The very grandiose and dramatic nature of the album and song are very fitting of a Stand made to grasp the power of The World.
Tohth: Just Another Day – The name comes from the Oingo Boingo song "Just Another Day" on the album
Dead Man's Party.
Tower of Gray: Fly on the Wall – The name comes from the AC/DC song "Fly on the Wall" and the album of the same name.
Wheel of Fortune: Mean Machine – I already gave this one.
Yellow Temperance: Nowhere Man – The name comes from the Beatles song "Nowhere Man," which is featured on the British version of their album
Rubber Soul.
...so the stand that is custom made for killing is not satisfied being used for anything else? That's not a limitation.
It is when it doesn't particularly care who it kills, and also when the SI doesn't actually want to brutally murder people, which will be most of the time, if for no other reason than to not be labeled a dangerous vigilante. Self defense and kill orders are one thing, using a Stand that constantly wants to stab through peoples' mouths and rip their tongues out as they tear through the back of the head, causing them to blood out while in horrible pain, would send a message that the SI would really prefer people not associate with him.
Personally, if it was about balance I would go with individual stands draining the user in different rates (like a stamina bar) and having to train each of them individually in order to bring said 'cost' down. Maybe add a small/medium/large cooldown or drain each time he changes a stand, also trainable. That way he has potential for absurd bullshit but doesn't allow him to pull counter after counter. Want to be Eidolon Plus? Hope you are ready to train like hell in order to git gud scrub.
Didn't it already say in the first chapter that stronger Stands drain him faster than weaker ones and that it slowly gets easier to do with only the ones he uses?
Yes. Specifically, manifesting a Stand for the first time is a big mental/spiritual strain (and it's specifically mental/spiritual because this way you can't just make it go away with Hamon or Panacea's powers), with "stronger" Stands causing more strain to the point that, at least currently, trying to manifest the most powerful Stands would probably be fatal, and others might cause the SI to just collapse. The more a specific Stand is manifested and used, the less strain is caused by manifesting that particular Stand. And, of course, Stands that already cause similar kinds of strain will still do so, like Star Platinum: The World causing heart problems and such.
Honestly the whole para humans seeing stands thing is kinda neat, and not that huge a deal concidering how being able to see sstands never means that you are safe from stands. I just hope you don't nerf the actual power of the high teir stands later on though, that would be pretty goddamn dissapointing and unnecessary.
Oh trust me, the fights toward the endgame will be a glorious parade of pure, unadulterated bullsh*t in true JoJo (and
Worm, honestly) fashion. "Gray Boy, meet King Crimson" is an idea I've vaguely considered.
Talking about powers though, will the mc be able to teach Hamon? I feel like that could be pretty cool naratively. On a more unrelated side note, I hope we get a interlude with the POV of some other character being baffled at the Posing of the MC.
As for the second thing, don't worry too much about it. As long as you present reasonably clear cause and effect in story (or reasonably believable bullshit) people will get it for the most part. Also Harvest is actually a really powerful stand from a strategy perspective, though not as outright offensively powerful as Bad Company.
I actually considered not giving the SI Harvest because of just how useful it can be with even a modicum of creativity (after all, in canon it proved a big hurdle for both Crazy Diamond and The Hand and even managed to survive for quite some time in a game of Cat and Mouse with Killer Queen), but I decided the SI needed at least one Stand that can be
directly dangerous as a combatant, and its use in easily collecting money meant I didn't have to focus
too much on the SI's mundane troubles of having no ID and no cash in this universe.