1. Is there any 18+ Content in this game?
Nope. There's handholding though, if that counts.

2. What is this game then?
It's like a drama/visual novel. Don't expect things to get too hot and heavy and you won't be disappointed.

3. Who is best girl?
Zheng Ziyan

Yep, that's all you need to know about the game.
Go ahead, approve your sons and daughters to play this game.