Leningrad's eyebrows are a stylistic choice, anime-like, iirc
Belles IIRC need crew to operate at 100%. They can aim, fire, and sail but they can't reload, repair, or put out fires. They need crew to work.
As for the Morg threat, the game timeline ends in 1945/1946 when the threat presumably ends. Meaning that as it stands there's no idea of what happens, it's up to the players
Stories, it makes it easier when you only have to manage the captain, the Belle, and occasional 2-3 other misc crew throughout the story. It's a stylistic choice, otherwise the stories would be massive I'd imagine.