At the moment I am thinking of some system where you quickly clear it with me before involving them, just to prevent anyone from doing anything over the top or that might go against the character or even change things in battle.
That being said so long as it fits with your character and the NPC, I am inclined to allow a good amount of leeway.
For example, say Unteroffizier Maurer is a complete and ardent Nazi, I am fine with a less "fanatic" character ending up in a fight with him. All I would really want would be a very brief/concise summary of what you intend to write.
Another example might be, randomly deciding that your character would in a lull during an operation decide to have a chat with Soldat Schmidt, maybe it turns out they are from the same city, etc.
Basically, I would encourage you to interact and figure out things that involve the NPCs and each other.
Weber has been modified into "von der Trenck" although in personality and ability he is largely the same. Upon reflection, it felt a bit silly that a high ranking officer would be as mysterious as Weber was.
Thorvald Larssen has been added to the character repository as well, just clarifying some things with Teo before I post his CS.