Hi HanSolo
So after several tests, I did not notice any conflicts in the game with this installation:
Conus' Graphic Mod 1.1
Lite Campaign LC 1.2_Fr
Terrain_harbour_flags_Mod_v1_2_1
Patch1_Terrain_harbour_flags_Mod_v1_2_1
Harbour Addition MOD V0.1
Harbour Addition MOD V0.1 - Open_Horizons
Cerberus62 Additional Merchant Ships 1.1 (Part 1)
Cerberus62 Additional Merchant Ships 1.1 (Part 2)
Cerberus62 Historical Ship Equipment 1.3
Installing different mods after...
Conus' Graphic Mod 1.1 is essential, to get the réalistic flags

Ignoring conflict in JSGME
Important: I not use Magnum opus
Very very good job HanSolo