Yes, it's easy to grow from seed. It even does well here in my clay soil. I have gotten seed from mine without a problem. It contains no gluten so, if ground and used as flour for baking yeast breads, it must be combined with another grain.
To cook amaranth seeds, boil 1 cup seeds in 2&1/2 cups of liquid - water or half water and half stock or apple juice until seeds are tender, about 18 to 20 minutes.