I bred bettas for years. It's fun, but you've got to be sure you're prepared for the vast amounts of water changes you're going to be doing on individual jars once the fry grow. Depending on personality, even many of the females will need to be separated. My very first spawn yielded over 200 fish.
Hydor sponge filters are the best, IMO.
You can feed newly hatched artemia to betta fry, but they're on the larger size that the fry can handle. If you want the best fry yields, you're better off starting with a smaller food for the first few days after the fry are free swimming. Microworms and vinegar eels are both excellent foods for this.
As for what to breed. It totally depends on what you're trying to accomplish. I would go with a quality half moon pair, as you'll have an easier time selling the fry. Mixing veil-tail bettas and half-moons is really not a good idea. Good selective breeding has been done to breed out of the half-moons the very traits you would be re-introducing by mixing a veil. You'll end up with genetically muddy mutts.
As for how high to fill the tank...I normally breed in 10 gals, and fill them half full. I would probably keep about 5-6" of water in a 20 gal.
