It's bad for a car to sit for a while without being started. So I would plan on at least letting it run for five minutes every few days. Cosmetically, you are faced with very few issues. But mechanically, it can cause future mechanical problems if a car "sits" for an extended amount of time.
Any moisture is hard on electrics, brakes, body work.......worst is salt air near the ocean, but eventually things corrode and rust. Sunlight - over a long time - will fade paint and upholstery and degrade plastics.
Modern cars aren't as susceptible as year back.......good for a number of years.......you can help with a coat of wax once or twice a year, putting preservative on plastic & rubber trim, headlights, tires.......spraying WD-40 or similar on parts that start to corrode. Extreme conditions as like near the ocean, it's worth taping up electrical connectors. In those conditions, the worst thing is to let sit for extended periods: brakes are most likely to be first thing to seize-up - so car should be "exercised" occasionally if not driven.
It depends on what type of car it is. But if you do leave it outside make sure you take all the gasoline out of it because sometimes things can damage the gas tank. Although it takes awhile for that to happen.
No, many people keep their vehicles outside. If it makes you feel better though, you can cover it or put it in a garage.
