This repo contain the grpc server and interface file for interact with Princess Connect: Grand Master client

Nope, It's not contain any service logic, but it might work if you implement the logic (specifically battle logic)

Maybe nothing, Just can communicate with client.

It contain 3 server (API, Matchmaking, BattleEngine) You have to modify the Princess Connect: Grandmaster to connect to your server by yourself

Maybe not, The battle logic is contain on the server, but also in the client While it possible to reverse engineering the client side logic, But it take too much afford to achieve it