Competition will increased because more organisms will be competing for resources
Gallons. You buy gasoline by the gallon.
No, what determines a dominant gene is how many copies of that gene exists within the parent. This doesn't mean it will be the most common because of recessive genes. It doesn't matter how many copies a dominant gene has, a recessive gene can still appear in the offspring.
More growth of flowers and or more plant food/water supply for it