Check out our Betta Care/FAQ stickies in the care forum. That should answer a lot of your questions about basic betta care.
When it comes to tank size, it's either you get a small tank (at least one gallon) and work hard to keep it clean, or get a larger tank, lose a bit of room, but not perform as much maintenance on it. There's honestly no inbetween.
If you don't perform frequent water changes for your tank, ammonia will quickly build up and poison and burn your fish. Not pretty.