Our own seeds from the Cow Shed Garden. We have hedgehogs here so the slugs and snails do not bother us too much. You might not be so lucky so you might need to protect from slug damage.
Ideally, grow in their final position, bury shallowly, at least 6 inches apart and keep damp. They would love some manure or fertile soil. They will need staking.
Or grow on a sunny window sill and plant out after all risk of frost has passed.
Companion Planting: Sunflowers can be used as a way to draw aphids away from other plants. Ants move their colonies onto sunflowers. The sunflowers are tough enough that they suffer no damage.