A glossed over aspect of interstellar society is the difficulty of accommodating humans (let alone aliens) comfortably on the same ships. I'll just deal with humans for this post.
Atmosphere is the first thing passengers will notice aboard a ship. Not being able to breathe trumps decor and cuisine. While passengers will be assured of a breathable mix, humidity, pressure, temperature and such will be for the crew (or captain's) norm and not theirs. This is because having your pilot or engineer become light headed at the wrong time may lead to inevitable and infinite delays in reaching your destination. Note that crew will usually forgo any atmospheric contaminants they grew up with (and acclimated to).
Passengers could have atmospheres set to their comfort zone in their staterooms. In some extreme cases filter masks or compressors might be worn. Contaminants can still become an issue. Consider most free traders and subsidized merchants travel to a number of worlds. The ship and the crew are exposed to all manner of dusts, pollens and pollutants which they then carry onboard. Decorative foliage is usually not a feature on most ships for this reason. Some pollens will send some offworlders to the hospital. But crew will bring back these various ticking allergens back onboard in their hair and clothes. This dust will accumulate despite air filtration systems if the ship is not scrupulously cleaned and your average crew will already be working two jobs on a tramp freighter. They probably won't get the corners or under the fridge.
Besides this consider that cargo is liable to bring allergens onboard or cause allergic reactions itself. Add to this gases emitted by plastics in a plethora of manufactured products from a multitude of worlds with different health codes written for variant humans with a variety of tolerances. You start to wonder how humans will survive their first trip without sneezing themselves to death.
An allergic reaction from a passenger or new recruit is almost inevitable. Hopefuly your steward has done a good job researching the passenger's files, identifying common allergens for their human substype and testing for such contaminants before they ever set foot on deck. And you thought your steward was great because he made awesome grilled cheese sandwiches.
That's the atmopshere. Let's talk food. Humans began ingesting dairy products a few thousand years ago. Despite what the state of Wisconsin wants you to think we as a race are not terribly good at digesting dairy. The same holds to a degree for grains as well. Humans are omnivores and meats, fruits, and veggies are where it's at (I sympathize as I am likely to be the first one to grab a mozzarella stick to eat with my pizza.) Consider then that some planets may produce food products for their inhabitants who evolved (naturally or otherwise) to eat the marginally digestible fare. Some may simply enjoy foods that are bad for them that others eschew or flee from. Having a dinner party onboard gets a little complicated when you have to feed the lactose intolerant, gluten sensitive, and bovine revering as guests and no one told the steward who just turned out his signature cheeseburgers (bacon cheeseburgers add at least another layer to the problem.) Finding edible and allergen free foods will be a challenge on some flights and it will be an ongoing nightmare at starports.
Experienced travelers might purchase a simple chemical analyzer designed to scan for allergens common to their race. Stewards could employ larger more sensitive shipboard devices (and might have to to be licensed to carry passengers). Captains and stewards will probably require a medical dossier on all passengers and crew for insurance purposes.
Lighting is usually not fatal (except to your toes when you lack it in the middle of the night). It is another element that can put passengers and crew off. People are evolved to make efficient use of the light emitted from a type G star but may evolve or be modified to see under the light of other stars. People from worlds orbiting class M stars will like light relatively dim. Those from hotter suns will like more light and when you mix the two types on, say, your bridge or drive deck hilarity may ensue. Passengers may also wave their high class status at you and demand you modify the light in their staterooms. Some people may have to wear shades or light enhancing gear to be comfortable.
These days people take artificial (electric of spin) gravity for granted. But it may be a problem to find a comfortable level for all. Many worlds are much smaller than Earth and don't have the technology to generate standard gravity in their inhabited areas. Subjecting people from low gravity to standard gravity can cause injuries and health problems. You can dial the gravity down but that may cause your crew to bounce around like spastic frogs till they get used to it (cheeseburgers everywhere!) As an alternative you could vary the gravity in different sections of the ship or make your workers wear weight belts. The problems are reversed for passengers from high gravity planets. They can usually stick to a standard gravity but then you get heavily muscled passengers bouncing off bulkheads and crew.
But if you really want things to get complicated just take on alien passengers.