as I mentioned before...all these questions were already answered in the link provided in my comment, which is posted / pinned at top of this forum section [know you can read...check it out ;D ] You really should check out other links here and posts...you'll be amazed at what you'll find if you take another 5 min to read / look further!
it goes into more detail then what Im going to say...but I'll reiterate it:
Favorite are blood worms. Available freezdried [like potato chips, or jerky] frozen, or live and moving!
Anything that says specifically betta is best, as they require meaty based foods. Some people suggest Bio-Gold [suppose to be really good] but mine never like it.
Alot of people will tell you bettas hate them. Mine dont. They actually prefer the flakes over the pellets. Mine are color enhancing...again, as long as stats meant for bettas. Tera flakes are not good, as do not support the diet bettas need: meat.
All depends on the available space you have. "Some people believe in 5 gallons as minimum. Yes, a fish can live in small tanks, but they thrive in proper conditions in roomy areas."
If space not an issue...try a 5.5 or 10 gal...your betta will LOVE you for it! I got a glass 10 gal tank from Walmart for under $10.
One thing to consider as well...if your betta should get sick, allot of betta / fish medications / treatments are pre-measured for 10 gal tanks [such as dissoluble fizz tablets]. One reason why I chose the 10 gal...but there are some ways you can get around it if want a smaller one.
There are many diff. brands and types: 2 prim types: submersible, and non-submersible. Submersible are the best. The box will indicate which size you should get, as they go by tank gallons. Mine heats anything from 10-20 gal tanks.
"These are tropical fish, and become very lethargic if kept in cold water. A light will not be sufficient enough for heat. In the night, temperature can easily drop 8+ degrees, which can kill as fish. Room temperature is not enough either. Hydor makes a wonderful heater for small tanks of 2.5 gallons and less. It resembles a heating pad and they work wonderfully while not being overly expensive."
Now one thing needs to be clarified: Bettas, unlike goldfish, do not require
filters to keep healthy...but it DOSE
help allot! Bettas need a light filter with low flow. They should have very little water movement in a tank. The filter will also help keep water clean. Size and type depends on tank size.