In my story, there is FTL Travel. However, many intergalactic travel times are still rather long. On a "cruise" from Betelgeuse to Triangulum that will take approximately four years, there are about 40 million residents aboard the ship, with no real majority species. All of them though, are humanoid. How would society be structured on this colony ship, if efficiency of the economy and low crime was a major priority? Species and their societies are as follows:
The Humans, the vast majority of which are of Russian and Chinese descent.
The Citrs, a blue-skinned race previously described in this question, most of the Tullusian kind, and their culture is very similar to modern American culture.
The Amethyans, and Orange-skinned race with four arms, large blue eyes, and very loud voices.
Many other races with less distinctly different features from Human, like Martians, which are just tall, hairless Humans.
Most people inhabiting the ship know the local standard language, an advanced version of modern Russian