IMO, it's not a great idea to keep one in a vase, unless it's at least 2 or 3 gallons (most vases aren't). Bettas like warm water and no matter what they tell you, they WON' T live on plant roots. They are insect-eating fish, so they do need to be fed flakes or bloodworms or betta-specific pellets.
In my experience, a betta seldom lives very long in a vase.
BTW, welcome to AC and fishkeeping!
Good luck!