Like everyone else, he wanted to be God.

For the right answer, we must turn to God's Word. It tells the whole story. Nothing in the Bible states that Satan was chosen as the perfect angel. Not one verse. He wasn't perfect at all. The Bible says sin was found in him, so he's far from perfect. He was jealous of God and wanted to take over the Kingdom of heaven, so he and some of the angels that he talked into following him, started a war with God and Satan lost, and got kicked out of heaven, all of them who followed Satan.

Bible tells us two important truths about evil that we need to remember. First, evil doesn’t come from God; He didn’t create it, and He doesn’t cause it. Evil comes instead from the Evil One — Satan — who is absolutely opposed to God and His goodness. It also comes from within our hearts, as we turn away from God and live only for ourselves. Jesus said, “For from within, out of men’s hearts, come evil thoughts, sexual immorality, theft, murder, adultery, greed, malice, deceit, lewdness, envy, slander, arrogance and folly” (Mark 7:21-22).

Second, the Bible assures us that God has already done something about evil! He sent His only Son into the world to defeat it — and He did. When Jesus died on the cross and then rose again from the dead, He confronted the powers of death and evil and Hell — and He defeated them. Some day the final battle will be fought, and He will come again to destroy all evil.

Don’t put your hope only in this world’s solutions. I assure you, they shall always disappoint you. Instead, put your hope in Jesus, for He alone is the answer to victory over evil and its consequences, and one day His victory shall be complete.

To gain his freedom.

Lucifer represents disobedience and the root cause of it. Satan is the id. " I want", " I need", " I will". The whole story is a way for primitive superstitious people to process the concept of man changing from a creature of instinct to a creature with the capacity for 'reason' and 'abstract thinking'. As a creature of instinct, you are not aware of things like 'nakedness' and 'dishonesty' or the difference between killing and murder. The sin of Adam is the side effect of reason. Evil. The id. We are indeed born with it, but it doesn't truly manifest itself in action until the so called "age of reason". The anthropomorphism of the id, Lucifer, saw power and wanted it. The millisecond, that thought entered the characters mind, it was cast out of Heaven along with any other celestial beings who harbored the 'ambition'. It's pure genius, and probably extraterrestrial in nature, but it's a fictional object lesson for homo sapiens in dealing with their newly evolved ability for abstract thought and reason.
Haven't you ever asked yourself about the 'omniscience paradox'? Doesn't it strike you as odd, that an omniscient being would constantly and consistently act as if it wasn't omniscient at all? It shows up right away, and becomes unnervingly obvious in Genesis 6:6, and then the non omniscient behavior continues throughout.
In my opinion, there is a supreme being and intelligent design, but it's pretty obvious to me that mythology is a necessary 'teaching tool' to give us some grasp of ideas that are, to this day, beyond our capacity to comprehend. Even extraterrestrial hybridization is touched on in Genesis, when the son's of God saw the daughters of men and mated with them to produce the Nephilim.

Did he? Or did he agree to help create duality so that through free will we could make our own choices.

We weren't good enough. You hear that? We're not good enough!

he wanted to be God & was tired of Praising Him

Power went to his head and he wanted control

It's all speculation. Why bother further speculating on the speculation?

If I understand it right, Lucifer was in charge of music. He wanted to be above God, but there is only one God, so, he was cast out of heaven. His followers with him.