well afaik their satan figure is not evil, and that Allah wasnt angry with satan after he refused to bow before him, but infact gave him dominion over the heaven and earth. they worship him because they believe Allah sort of washed his hands of the world and the immediate point of contact is Satan. Greeks had a similar view of the ultimate God, so do Christians (the Father being the ultimate creator, Jesus being his gateway of sorts). they were influenced by Christian Gnosticism, which includes some amount of ethical monism i.e. not viewing things as externally good or evil but an outcome of human nature so dont blame Satan for humanity’s fall.
no idea why they associate the peacock with him, possibly because its a regal bird, and they make this deity out to be very regal. then again certain branches of gnostic christians (Ophites) worshipped the serpent, so it could have something to do with what you say.