I mean the classic librarian character would be Wizard, though Arcane Trickster seems like a great choice, especially for a game of crime and intrigue and what have you. It’s true Rogues are damage classes in combat but you could rely on a bow when you’re not slinging spells.
Maybe the dark horse choice could be Warlock with the Old One patron? They’re all about cosmic horror and the mysteries of the universe.
I got no idea what a grung is (well I mean now I know it’s a frogperson), I guess you could choose class based on what ability score bonuses it gets.
As for your glasses thing that’s adorable. I don’t see why you’d need a corresponding benefit necessarily, I think loading your characters with flaws is fun on its own. Floating modifiers like “-4” are discouraged in 5e (notwithstanding I’ve just written a bunch of combat realism tweaks that reintroduce them cause, you know what, fuck it), you could probably just say disadvantage on attack rolls, or that it imposes the Blinded condition.