As for speed:
I'm going to assume that the distance between the starts Buu destroyed are the same distance between Earth and Proxima Centauri or
4.2465 lightyears
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Low end: Assuming he do this 10 years, and there are 100 stars (lowest number for hundreds):
D = 100 * 4.2465 = 424.65 light years
V = 424.65 LY / 10 years = 42.465 c or FTL+
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Mid-Low end: Assuming he do this 10 years, and there are 500 stars (middle number for hundreds):
D = 500 * 4.2465 = 2123.25 light years
V = 2123.25 LY / 10 years = 42.465 c or Massively FTL
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High-Low end: Assuming he do this 10 years, and there are 999 stars (highest number for hundreds):
D = 999 * 4.2465 = 4,242.2535 light years
V = 4,242.2535 LY / 10 years = 424.22535 c or Massively FTL
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Low-Mid end: Assuming he do this 5 years, and there are 100 stars:
D = 100 * 4.2465 = 424.65 light years
V = 424.65 LY / 5 years = 84.93 c or FTL+
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Mid end: Assuming he do this 5 years, and there are 500 stars:
D = 500 * 4.2465 = 2123.25 light years
V = 2123.25 LY / 5 years = 424.65 c or Massively FTL
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High-Mid end: Assuming he do this 5 years, and there are 999 stars:
D = 999 * 4.2465 = 4,242.2535 light years
V = 4,242.2535 LY / 5 years = 848.4507 c or Massively FTL
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Low-High end: Assuming he do this 2 years, and there are 100 stars:
D = 100 * 4.2465 = 424.65 light years
V = 424.65 LY / 2 years = 212.325 c or Massively FTL
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Mid-High end: Assuming he do this 2 years, and there are 500 stars:
D = 500 * 4.2465 = 2,123.25 light years
V = 2,123.25 LY / 2 years = 1,061.625 c or Massively FTL+
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High end: Assuming he do this 2 years, and there are 999 stars:
D = 999 * 4.2465 = 4,242.2535 light years
V = 4,242.2535 LY / 2 years = 2,121.12675 c or Massively FTL+