Jonathan,
Welcome to Subsim. You will soon learn just how much this game has changed since it came out. There is a deep knowledge base lurking within these rooms so if in trouble ask (tactics, mods, why, how, when, who, what)
As for mods start looking, I recommend GWX and GWX patch. As for other mods there are many to select and all the modders here are a great asset to this forum.
A good place to learn the history of U-boat warfare is this place:
http://uboat.net/
Once again welcome to the world of Subsim.