Yes, if said player is captain, has a long contract and you want to negotiate an exit. And there's also the issue of registering other players.
Informed? Seemed more like "informed" trough the media, like everybody else.
That doesn’t matter and I doubt clubs do that in advance.
Players are usually informed that their team want to move on when they have a replacement signed.
The club don’t need to inform any player of anything beforehand.
Ter Stegen fwiw also has the right not to release his medical information, but I don’t see how this will help him if the club in turn refuses to let him leave in January to prepare for the World Cup unless its a permanent transfer.
His NT coach have already said he needs to play to start for Germany.
Would be in his best interest to play ball and negotiate a smooth exit in January even if its on loan.