yeah any of those games mentioned are great to look into for visual inspiration and like Exploreable examples of the types of environments. since splatsville is intended to be a poorer more run-down foil to inkopolis, this new place may be somewhere more in the middle. Not super affluent nor the heart of emerging youth culture, just something thats kind of There. Perhaps its averageness could be what makes it stand out as part of the point? A forgettable location that most people just pass through contrasted by characters that Arent That.
now map location-wise hmm... it'd likely be in the splatlands- where ppl have eaten the salmonid-are-bad propaganda rolls but not to the point where one cant just vibe out somewhere or somewhere entirely new. Inkadia has some STRONG anti-salmonid stuff going on between the physical blockade to a tiiny little bit of flavortext that was (i think only) in S2's salmon run handbook about how theres laws against "unauthorized" interactions with salmonids. it was probably included as a nod to how Extremely Sus grizzco was just like as a physical space in S2 and how doing a shift there is almost certainly against the law but like maybe they found a gray area? who knows. its bad!

though of course there is the secret fourth possibility of them living in a salmonid city. We've mostly only seen Remains of them or of contested forts (and uh an arena) but weve seen enough to know that there are portions that are above-water. Personally my hc is that they are a sort of amphibious city in how its built. Some buildings are above water only, some are below water only, and others are built with a hatch that moves between the two. now then its a matter of how the inkfish got there and like. there are absolutely ways especially with how salmonids have a generally more positive relationship with octolings, particularly those from the domes but I like to think it extends to more than just octarian octos bc of second language learning classes being taught so communication is easier.

im typing all this before bed so like im doing myself (and perhaps you as well) a favor and im going to come back and tackle the character side of things tomorrow. in the meantime if you have any more deets feel free to dish (heh) them out

and as for my credentials (aka look at my ocs aka bragging zone):

https://toyhou.se/AutumnWyvern/characters/folder:4757862 (oooh i forgot to include Russell and updoot Sunrise accordingly... ah... 2morrow...)

https://autumnwyvern.tumblr.com/post/760129072196157440/autumns-cool-general-inkfish-biology-hc-post-that

https://autumnwyvern.tumblr.com/post/754293684957331456/exploration-of-using-fonts-to-convey-languages-ft