I am not 100% sure about this, but I think marinating the herrings in milk is to make them even more tender, but also to reduce the salty taste a bit. Herring can be very overwhelming in a dish.
I’m not sure about the smoked ones tho… Maybe you should taste the smoked ones before marinating them. If they are mild and soft in taste you don’t have to marinade them.
For my own personal taste I wouldn’t go with a berry sauce with it, but a dill or a soft dill-mustard sauce. But that’s my personal taste
these are 2 different cheese creams! one (goat cheese, chive and almonds) fills the mortadella rolls, the other is made with gorgonzola and walnuts and it’s presented inside endive salat