Is Satan essential to Gods plan being carried out? And if so, is God responsible for the creation of something evil?

Speaking from a mormon mentality. But not necessarily a member. Looking for ideas from all Christian denominations. The mormons preach in the pearl of great price, that in the pre earth life, all of humanity gathered to discuss the plan of salvation with god. Lucifer and Jesus came forward and shared their thoughts. Lucifers plan was ultimately shot down and it is said he became prideful and was cast out. Some of the other angels followed him etc etc. My question is this. If "all good things come from god" as said by mormon prophets, then how was an angel in heaven able to experience pride and turn away from god before being subject to the "natural man" state of temptation? And second, if in order for God's plan to work, Adam and eve had to partake of the apple and give into sin, then SATAN HAD TO BE PART OF THE PLAN. Therefore God orchestrated it. Which in turn makes god responsible for creating something evil right? Asking for answers from all views. Against mormonism for mormonism, whatver your thoughts are.