i] There is chlorophyll-b (yellow-green) and carotenoids (yellowish).
ii] The green chlorophyll isn't an evolutionary mistake (unless, of course, you take the viewpoint that evolution IS just mistakes). Plant's get plenty of sunlight. The sun is way stronger than indoor lights used to grow plants. They don't really need more energy from the sun. Plants actually have some pigments to dissipate light because they would otherwise absorb too much.
iii] Plants might absorb too much energy. Think wearing all black on a hot summer day, and standing out in the sun ALL day.
iv] Plants don't really use ultraviolet light as far as I know. With the ozone layer blocking most of the ultraviolet rays coming at us, it would be very strange if they did evolve to absorb ultraviolet light. This might also harm the plant. Infrared rays do reach plants, but they don't really do much to help in photosynthesis. Anyways, light has to travel through the cytoplasm of plants which is full of water, and visible light is best at travelling through water.