I'll start with appearance and then personalities:
Alicia: I can't say she was inspired by any specific person, just an overall combination of Hispanic and Native American traits with the added desire to give her a rather doll-like appearance, which adds to her damsel image, and will throw that damsel image when pretty and shy is no longer the only side of her readers get to see.
Her personality is in someways inspired by me (numb and rather depressed at times, and thusly unmotivated, especially for self care, yet also creative. Very messy. Body image struggles. Abandonment/mommy-issues and trauma, etc.) Other parts of her personality are more based on people I know who have suffered from social anxiety and such.
Kattar: Visually is inspired, again, a lot by Hispanics I've seen in my own country (though Mexicans look very different from us generally) as well as Korean features, such as his very slanted eyes and sharp nose. (this portion of his appearance was inspired by Hwang Hyunjin, but his complexion (at least when he's healthy) is much browner, courtesy of his Mexican mom.)
His personality is not inspired by anyone I can trace, at least at the moment, though parts of his trauma are, again, inspired by my own, or that of people I know personally, which definitely inspires his actions. So perhaps I could say his desire to prove his mom's opinions wrong is also based on myself.
Something of a character description for each of them can be seen here: https://tapas.io/episode/3049986.
And here: https://tapas.io/episode/3026452
Jinwoo's physical appearance was inspired by Yoon Jeonghan. That's basically it. Though it was also designed to reflect the dichotomy of his character - silver hair but wearing cute baby blue sweaters, and accessories with cartoon faces on them and such.
His personality was largely my own imagination: love for fairy tales, art, cards, etc. But in part it's based on one of my cousins, the son of one of my mother's teachers, and people i've seen in videos online.
Kimberly's physical appearance is inspired by pictures of blond haired Melanesian people I saw years ago that stuck with me, as well as african american traits and features. though her fashion statement was designed to reflect her princess-y role in the story.
Her personality in a lot of ways is made up of parts of my own, but since that's a bit of a secret, I can't spoil it yet.