Question: If Lucifer was one of the most beautiful angels in Heaven, and Heaven is a perfect place without sin, how did he sin against God in Heaven and become a fallen angel with many angels following him?
Answer: The short answer is, “I don’t know.” You have made some assumptions here, which I mostly hold to myself. Satan (the term “Lucifer” may not be the correct translation of Isaiah 14:12; most modern translations translate “morning star”) is probably not the one being openly described in either Isaiah 14 or Ezekiel 27, but is apparently a created angel who somehow chose to rebel against God. Remember, earth was not in a state of sin either, and Adam and Eve did not have sin natures, and yet they both rebelled. The how of this is a mystery that the Bible does not address, either in terms of Satan or our first parents.
And why did many other angels choose to follow him? We don’t know. But the original temptation he made to our original parents was that they might have the right of self-determination and not need God’s guidance. There is something in us that still struggles to trust God with everything He determines for our lives. Something in us still wants to have the control, thinking that we would make better decisions about our lives than He would. This is the lie that has led the world into chaos and tragedy for all these millennia.