Dear Hans:
The SH4 Project looks fantastic. I recommend you the SH4 1.5 /with U Boat mission), install Lurkerīs Operation Monsun and take a look at this mod. There is a lot to study in this mod (campaign structure, ships imported from SH3, GUI, etc.). Also, you can try the Nine-Delta_Two mod by Ducimus, an improvement from stock U - Boat Mission with a Type IXD2 with interiors and crew.
I think there is a lot of possibilities in SH4 for an Atlantic Campaign and a supermod HAHD in the 1.5 version!
I continue in the work with the tutorials and texturizing ships in SH3. These ships are easily convertibles to SH4. I installed a good quantity of VonDos ships to SH4 (TMO Pacific Campaign), and scripted in the campaign. No problems...
Best regards.
Fitzcarraldo