Okay so, firstly people cast out by their families or shunned could work, since there are some anti-dragon human factions (and anti-human dragon factions). Apparently the majority has an ambivalent view on it, but it could be seen as weird, since, well, dragons are a lot stronger than you and just as intelligent, if not more-so
Also going by canon, people would be raising only a few dragons at a time, and just the eggs take years to hatch, not to mention the growth progression from hatchling to adult, so I'd imagine there's a maximum of dragons allowed in RP, BUT you can select from any of the ones you own, that sorta dealio? With restrictions of course... Since, uh, the Guardian of Nature dragon is basically god, and the trio of summoners are also highly respected users of their element, and those Avatars you can get from breeding the GoN are also like gods....
Basically= GoN is Arceus, Magma/Ice/Thunder are the legendary birds, Avatars of Change/Creation/Destruction are like dialga palkia giratina, the holiday dragons are basically embodiments of their holiday (especially the christmas ones), etc, you see what I mean by this, these are special dragons and there'd be limits (more case-by-case basis with holidays tho)
So... Also to be true to lore, the dragoneer/tamer person would have to be of a good age (twenty? thirty? fourty?) to have had taken an egg and raised it from egg to young adult/no longer a hatchling, with their dragon raising career starting at a young age, with variation in the growth progression of different species of dragon in mind. HOWEVER they could have found an abandoned hatchling, OR befriended a wild hatchling/adult, OR found an egg close to hatching, and that could lower that age requirement for being a dragoneer that is affiliated with an adult.
(personally I prefer the term dragoneer, since tamer implies the dragons are nonsentient animals, and implies a mastery over them, when in reality humans and dragons are more like equals)
Ofc, there's multiple ways you could go about this when character building-- Was this person orphaned at a young age and a dragon took pity on the poor thing, so the dragon raised them as best it could? Did this person's family take up the very rare and unusual profession of raising dragons, so they were already affiliated with a small family of dragons from a young age? Is this person older and thought to raise metallic or poach-able dragons to make a profit, but perhaps didn't have the guts to snuff out the hatchling, so they befriended their former quarry and kept in touch as the years went on? Is this a younger person that's still raising a young dragon? Did that younger person perhaps take home an egg or a few like any other overly curious child and is now burdened with raising a bunch of hatchlings due to that poor decision way back when? You can sorta get the gist that keeping dragons isn't super common, and that the dragoneer may get a bit (or a lot) isolated from their community due to living this second life as a caretaker or friend to these reptilian outsiders.
Also, in regards to geography, on that map you get when you open the homepage on the Dragon Cave game, the central continent with all biomes on it is Galsreim. Apparently there's a "republican monarchy" goin on there, with a king or queen and a bunch of elected officials making the law. Think older European countries, that had both a (political rather than only figurehead) monarchy and a parliament going. The age is sort of medieval, maybe a touch of renaissance... Basically, the primitive gunpowder pistol exists, but not a musket, and steam/electric power isn't a thing. However, mana and magic allowed for a different evolution of technology, with say, airships powered by air magic fueled crystals of air mana, and using light spells/enchantments on crystals or something to create light mana fueled indoor lighting.
I mean, mana potions or raw mana crystal lamps aren't a thing, since, y'know, painful mutations into a non-human after exposure that will likely result in being shunned or killed as a monster. But, life mana being used to fuel spells that heal injuries and cure disease are a thing, so you wouldn't have advanced medicine and doctors, you'd have advanced white magic spells and wizards.
Also, there isn't really fleshed out cities in canon, like, there's nothing that's been fully confirmed by TJ. But, taking the model of Ye Olden Europe, while there is a monarchy-republic and cities going on, there are still peasant villages, or at the very least rural towns. So, yeah, an unofficial village for the dragoneers could fit, but it'd be rather out-of-the-way. Also, in regards to your floating island thing-- those do exist! Bad side to it, they're chock full of air mana crystals, so permanent human settlers would most likely be mutated into a non-human birdbeast people within the first or second generation of kids born on the island. BUT, dragons wouldn't be so easily mutated as they have a kind of mana tolerance, so... Perhaps dragons could explore and bring loot?
Also, almost forgot about mana and magic and the science of it.
Okay, so, there's 2 planes of existence- incorporeal, and corporeal. Inco in the the soul-ar plane, where it's just souls and their soul energy and then a ton of magical energy of different varieties. Corporeal is the physical world, the mortal coil- it's what you see and exist in. Living things with souls have, well, a soul tied to them. The living body has a tether to their soul body that is near inseparable by use of magic, there's no soul-separator spell. When you die, that bond is cut, and you get a dead, soulless corpse, and then a free-roaming spirit. The soul requires a tether to exist permanently, as without a body, it lacks an identity, memory, or anything to keep it grounded in existence. After around 2 weeks' time, a roaming soul stops existing, typically. Maybe you get a few permanent ghosts, but I doubt they occur naturally in this process.
There are two types of magic, active and innate. Active uses mana (the corporeal material that releases magical energy as it is used, and physically dissipates as it is used) to release magical energy into the soul-ar plane, and then to enable the tether between soul and body to channel magical energy into the physical world. That magical energy then turns into the result of a spell. Certain mana are used to create certain magic, with death mana being used to make death magic energy that is then used to create death-aligned spells. Light mana would be used to create light magic which is then used to create light-aligned spells. Innate magic, from what I can understand, uses magical energy that is already in the physical plane of existence, rather than taking magic out of the incorporeal to the corporeal plane. Naturally magical creatures, or creatures mutated by magic, all can make use of innate magic acts- telepathy is an act of innate magic, I assume similar of fire/ice/lightning breathing, or the White Dragon's passive ability to heal its own minor wounds, or the Cassare dragon's passive ability to deaden active magic within a given radius of its body. However, the Black Dragon's practice of black magic and hexes is active magic, as are any human magic acts, as they are unable to use innate magic.
Also, in order for humans to use mana without risk of mutation or illness or whathaveyou, mana is refined into a less-potent-but-less-dangerous form. Apparently the process isn't elaborated on. //sigh
Anyways, that's all I got for now-- expect me to post more adding onto this