I never understood how Lucifer's rebellion even happened. Didn't God only give free will to humans? So how could any of the angels do anything against God's will? And if that's correct, God set Lucifer up to "rebel" just so he could cast him out?

And if "everything is according to God's will or plan", then God is responsible for all the bad things that happen too. You can't blame anything on the devil because Angels don't have free will and everything is part of God's plan.