These 3 mods are the basis for any others I add on top of GWX:
M.E.P v6 for GWX
German U-Boats Compilation
RCB's SH4 effects GWX 3.0
Just a warning, M.E.P v6 makes the sea look amazing and also makes the game much more of a challenge as you can both see enemies at a longer range and they can see you too!