re: A sunshade as big as a planet, covered in solar power modules
Since Venus is roughly the same size as Earth, a sunshade big enough to block all the sunlight could also collect 3 million exajoules of solar energy annually. Using your energy numbers, it would take 17,000 years to completely strip Venus of it's atmosphere, but only a few thousand years to strip away enough CO2 to make it "livable", perhaps "survivable" would be a better word.