I don't have it myself, but I guess I can answer your questions :
1. Yes you can, Sir, that's for sure. Read this post from Onkel Neal :
http://www.subsim.com/radioroom/showthread.php?t=131756
2. I don't think so... There's no need to separate files, at least sounds.

(there's no need to separate english and german sounds for the 2 different versions of the game, as the add-on got the english voices).
3. Get german voices via the link in the 1st post of this thread !