tamamori is my favorite. I think he very realistically depicts mental illness and I enjoyed reading hashihime through his perspective especially because he was so flawed and even evil at some points. I saw myself in certain aspects of his character and it's very rare for me to be able to relate to characters at all, but even if I didn't have any relatability with him I would like him.

oosaki is probably next even if we haven't seen much of him. I love how quietly insecure he is and how he seems to have a really soulful inner person, and he's effortlessly funny just because of how he misses some social cues. I also really love stoic characters who show their kindness for others physically rather than verbally like how he puts himself in harms way so easily for others.

then comes choutsugai. tbh the main reason I like him so much is because he's an asshole and comedically mean. I love his running gag of attracting every pervert in a 50 mile radius while himself being almost a little bit of prude. I had the most fun with chapter 2 out of the other uruc chapters because of him.

then shou-chan. I like how he's down to earth and so cut and dry at some points. no bullshit, no nonsense. he's kind and sweet and his love for akira is cute.

then juurou. tbh I couldn't really get into juurou. I'm not sure why, usually he hits a couple of my niches, but I was more interested in the icaruses in his route than him or his romance with yomi. sorry to yomijuu lovers....

funnily enough it all comes back to dogra magra. funeno's given name is kureichirou, and the protagonist of dogra magra is named kure ichiro. one of the central conflicts in dogra magra is kure ichiro being admitted to a mental institution for a crime he is being accused of that he cannot remember committing, and over the course of the novel he slowly falls more and more into madness as he tries to determine what about him is real and what is a lie that was fed to him by a crazed doctor overseeing his case. We'll probably see this be present in funeno's character, as his hannin line (a dialogue snippet following an accusation levied against a character. all of the attendees have a hannin line) featured in the initial settings booklet and the ooe cool-b features was 「わたくしなのでしょうか？わたくしかも知れません」, or "is it me? I don't know... it could be me." which seems very similar to his namesake. I wonder if funeno himself doesn't know if the crimes he's being indicted for are true. I would love it if that's a big theme with his character- struggling to figure out if anything he's being told about his crime is real, all while fighting guilt for something that might have been completely fabricated or exaggerated. it's fun to think about!

I'm not sure what to expect with toyosu's route considering it will probably be shorter than a lot of the other characters, but there are a few implications about his character from the inugami curse that I'm pretty interested in. all of the daiba family's names come from the inugami curse novel (shizuma's father sahei is named after sahei inugami, the family patriarch, his brother is named after sukekiyo inugami, one of sahei's grandsons, and shizuma himself is named after shizuma inugami, another grandson). in the novel, sahei inugami had a very close relationship with a monk named daini after this monk had taken him in and raised him as a child, and the two became so close that their relationship was rumored to be homosexual in nature by those in their neighboring village. their relationship was so intimate even that daini's wife ended up leaving him for a period of time. they continued to be entangled for the rest of daini's life, and the monk continued to have great significance on the dealings of the inugami clan.
all this is to say I wouldn't be surprised if toyosu is modeled after this monk, daini. and this is very interesting to me because it implies that he might have close relations to ooe's inugami clan, the daibas. he's already been depicted in a piece of artwork with a motif usually associated with shizuma, the peacock, so I wonder if that will go anywhere... additionally, in the demo toyosu seemed particularly fond of hinode and watched over him when things became tense, and I remember in his seiyuu announcement teaser he was also standing next to hinode in a way that suggested he was still watching over him. I'd like if they continue to be intertwined... because it's cute of course, but I might see hinode becoming a sort of achilles heel for him. just speculating!

this is a really interesting question because, like you said, some of them would make sense to see in universe (ariake eyeshadow, shijoumae scar, oosaki eye bags etc) but others would be really... strange. funny to think about funeno dying his eyebrows red every now and then for whatever reason. ooejima fashion fad...?? maybe all of the markings are diegetic but they just appear to be colored normally to those around them. for example... daiba and oosaki both have markings under their eyes which contribute to their visual similarities, but daiba's just appear to be normal eye bags while oosaki's are colored red. in universe it would make sense for them to both have this feature, but oosaki's just resemble daiba's in color. I'm of the opinion that the markings definitely have significance outside of just character design. I wrote an analysis thread about how I feel the red highlights in shiodome's design served to specifically highlight his ears, which contributed to his established motif of see no evil, hear no evil, speak evil. I personally theorize that takeshiba's crime will end up being related to his family's deaths by fire, hence his red markings accentuating his eyes— to indicate that he saw something that had a significant impact on him. so on and so forth. and yes I definitely feel the red eyes are indicative of who in the cast are criminals and who are not. kurosawa is really fond of storytelling through eye color, so the fact that only the side characters have black eyes wasn't lost on me.