I suggest grabbing up Dangerous Waters AND the Naval Combat Pack. That way you get ALL of Sonalyst's excellent sims.
For Dangerous Waters, make sure you get the LWAMI mod version 3.08:
http://www.subguru.com/DW_missions/LWAMI_308_Full.zip
and the Sakura Mod v1.02 (Be sure to read the instructions included with this one for using it in your missions)
http://savefile.com/projects/808585583
This mod will be added into the next version of LWAMI when it's finished (And so far, it sounds like they're doing a bang up job of it, incorporating the entire SCX database, not to mention the communication satelite mod they're trying to perfect.

).
You may also want to check out
www.subguru.com if you're looking for missions and downloads. There's a LOT there. "Red Storm Rising" for DW is especially good and I have a soft spot for "Sicilian Wedding".
There's always people here interested in playing multiplayer. Just ask and you'll find people. I'm always up for a game when I'm not busy running around.