Most bras have 2 hooks per column. Some small bust ones may have 1, while larger bust ones might have 3, occasionally 4. Longlines have 5-6. The number of hooks simply depends on the style and design of that particular bra.
More hooks do help with support since it usually means that the band is taller and can therefore distribute the weight of the breasts more. Most of the support is meant to come from the band with only a little bit coming from the straps.