A betta should be kept in no less than a 1 gallon container. Many breeders use Beanie Babie containers or quart mason jars, but these fish also get water changes multiple times a week. The larger the container, the less water changes you have to do, and the happier your betta is.
When you get up into the larger tank sizes, like 10 gallons and up, water changes are greatly reduced. Ten gallons also allow for the addition of more fish, if you desire. A community tank (multiple fish) should be no smaller than a 10 gallon. Most freshwater fish (besides guppies and teeny mosquito fish) require a minimum size of 10 gallons. In 10 gallons, the tank can cycle (bacteria grows that will turn ammonia to nitrite, nitrite to nitrate, and nitrite is plant food!) and you can have several fish (depending on the species you prefer), or even several bettas if you desire.
Bettas are tropical fish, and therefore do best in a water temperature between 78 and 82 degrees. Bettas are very sturdy and can handle water several degrees above or below these temperatures, but it is best to have them at a stable temperature. Using a heater in your tank will help keep the temperature stable. Aeration is not required. Since bettas are anabantoids, or air breathers, they rise to the surface to gulp air.
However, if you wish to keep other fish in with the betta, aeration is needed. Aeration does not actually provide oxygen, it agitates the surface of the water to increase the waters oxygen level. If you have a well planted tank and a low fish load, aeration is not needed due to the plants providing oxygen. But for begginners, and for those who don’t want to risk fish suffocation, aeration can still be used.