To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as an evoke cost), add any cost increases, then apply any cost reductions. The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.

Vibrance's first and second abilities check to see if at least two mana of the appropriate colors were spent to pay Vibrance's cost. It doesn't matter if more than two mana of that color was spent; the effect isn't multiplied.

Vibrance's first and second abilities care about what mana was spent to pay its total cost, not just what mana was spent to pay the hybrid mana symbols in its cost.

If this spell is copied, the copy will not have had any colors of mana paid for it, no matter what colors were spent on the original spell.

If you pay the evoke cost, you can have the creature's own triggered ability or abilities resolve before the evoke triggered ability. You can cast spells after that ability resolves but before you have to sacrifice the creature.