Most likely not. There's no indication that Adriana Lecouverier is based on a true story. It could just be a fictional creation to engage the audience.
It's hard to say for sure. The availability of Venti in the story depends on multiple factors such as the story's genre, setting, and the author's intentions. It could be possible, but you'd have to look closely at the story's details to know for sure.
Well, in a Venti identity reveal fanfic, it could involve Venti dropping his carefree bard facade and showing his more divine or ancient side. It might include scenes where he has to use his true powers to protect Mondstadt from a great threat. And this could lead to a whole new understanding of his character by the people of Mondstadt and the readers of the fanfic.
I'm not familiar with this 'vince gill pretty little adriana story'. It could be a personal anecdote, a fictional story related to Vince Gill and Adriana, but without further details, it's hard to say more.
Another possibility is that it could be a normal citizen of Mondstadt who has a special connection or intuition. This person might not be as powerful or important as Jean or Diluc, but they could have a moment of realization. Maybe they see Venti do something that defies normal human capabilities and start to suspect that there is more to him than meets the eye.
One possible plot could be a curse placed upon him by an evil sorcerer. Maybe he offended the sorcerer in some way, and as revenge, the sorcerer uses dark magic...
One book that might be similar is 'To Kill a Mockingbird'. It also delves into themes of society, human nature, and growing up in a particular setting. Another could be...