So the three LIs with mysteries, it seems pretty straightforward to me.
Miranda: is Miss E. She lost her voice to an illness recently, and that's why she had to do a career change. She even reacted when Danielle mentioned having rock stars around.
Taylor: her parents died last year. That's why she had to drop out that year, and that's why her parents 'went back to Europe,' to be buried. She's sad and doesn't want to talk about it.
Sana: she's almost certainly the kid of a crime family and Viktor is her bodyguard. I would be happily surprised if that was somehow avoided, but seems very straightforward.
Hard to pick a current favourite LI, which is a good sign (though managing all the branches can be a pain). Lana was an early lead, but didn't really like her character redesign for chapter 2 (or some of the other redesigns), and since then she's treading water in easy lay territory. Rose has that best friend connection, which is a trope that often pays dividends. Mirabella is my current fav of the classmates, just too damn cute and her hair when it's not coiffed is amazing. Elsa has the lead for staff, though Danielle is stepping on her red-head territory, but haven't seen enough of her. Taylor seems like one of the best matches for the MC, values wise. Chemistry seems to be there as well. Samara is hot, but I don't know if she's an LI (same with Fang). Olive dances on that line of adorable and annoying, and I'm not sure which she'll radiate, line by line. But I can see the appeal.
No one else seemed like a good long term option, but they all seem great for a few flings.
It's a game with promise.