Then there are the big ray flowers on the outside that are sterile, but are useful for attracting insects. Bees are the main pollinators, but Monarch butterflies also love to feed on sunflowers. Sunflowers need quite a bit of room, so space them one to three feet apart. Their roots produce a growth-suppressing substance to foil the weeds, so it doesn't work too well to grow beans up the growing stalks. If you want to grow beans on them, leave the stalks in the ground after harvesting the seed heads and then plant beans around them the next year.
All varieties readily cross with each other.
So try to provide a half mile of isolation to insure purity. The flower heads follow the sun when they are still receptive to pollen or still shedding pollen. After the seed is set, they no longer move, and cross pollination is no longer possible. Rogue as soon as possible to prevent any pollen from off-type plants crossing with true, healthy specimens. Take out any plants that display leafy bracts coming out of the center of the head and any that have small flower heads coming out the back of the main flower head.