I highly recommend joining the Discord: https://discord.gg/RJeV2qu28J
There are modders who have made all sorts of characters.
Just drag and drop your favorite 8 in a folder and they're in your game with no real fuss.
In particular, I'd recommend CrimsonIcarus' characters if you want low-key villagers who feel like a natural addition to the existing population.
So you just want the custom characters in the base game to include a much longer list of options?
Hmm.. that's on ThreeES then if you don't want someone else handing you the files. There's a decent manual being written (in the discord) if you ever want to spend the wait time in just poking around at making your own thing. But, worst case, if you want to do no making, and trust no one in sharing a premade file with you except ThreeES.. I guess, I hope it works out. More is good.
The characters/npcs thing sounds like you want Silverpine to be expanded. NPC's would mean homes, buildings, businesses, and canon. Unless the developer has a similar feeling as you about the town needing to grow, and an interest in your species ideas... That sounds like it would be a much longer way away from implementation.
Or, having ThreeES absorb certain DLC/modded content and publish it directly on these itch.io pages? Maybe that's the single fastest option, but a big IF to ask the game's developer to switch to content publishing.. Although I really do love the game as it is right now.