Ahoy!
Check the sticky at the top containing guides for sonar, TDC, etc. This will help with the manual targetting in 100% realism.
As for mods, there are a few popular supermods out there that really improve the game from stock. I think they all require the U-boat addon which patches the game to 1.5.
The supermods I know about are:
Trigger Maru Overhauled (TMO)
Real Fleet Boat (RFB)
Operation Monsun (OM)
Run Silent Run Deep (RSRDM) - this is a mod for historical shipping traffic and major battles.
You can find info about these in the sh4 mods section.
Welcome aboard
