It's nice to see people doing research before they buy the fish!
A 2/2.5 gallon is the minimum for bettas. You'll need a heater for him-his water will need to be at least 74 degrees. The optimum range is around 76-80 degrees farenheit.
You don't need a filter, and it people say it's difficult to cycle small tanks. Your bowl should be cleaned out probably twice a week. I have a 2.5gallon myself. I do a 50% WC on Wednesdays, and 100% on Fridays where I also take out the plants and decor and wash them.
Live or silk plants are preferred for bettas. You can pick plastic ones, just make sure they're not sharp or rough-they'll tear your bettas fins. you should also provide a hiding place for your betta.
When choosing a betta, look for a healthy one. His fins shouldn't be frayed, torn, or curled. He should have a good, vibrant colour. Laying down or floating on top of the cup isn't a good sign. He should have clear eyes that aren't bulging.
That's all I can think of at the moment. Good luck!