You had a lot of nice ideas! I won't repeat what others have said, but you should definitely keep it up and keep learning! Welcome to Godot :)
Oh, for whatever reason, the first time I played, the transition after billy disappeared would not trigger. I reloaded, and it worked the second time. You also had collisions on the speech boxes :P I think if you use the CanvasLayer node instead, that will take care of that.