From what I know, there are twelve angels in heaven. Satan is the thirteenth angel. God expelled Satan after he attacked the other angels. God created the universe and put Satan inside, he can never escape. I know that doesn't fit with Bible stories. In Rev. 12, Satan and other angels fight Michael and his angel. I had a dream about Michael. He was high up in the air in a large room siting in an arm chair, he was wearing an army generals uniform. A voice said, "This is Michael, God's General of the angels." I don't believe God will ever create another angel.
Angels are God's servants. They watch what is happening on earth and report to God. In heaven, angels surround God loving and worshipping the two Gods in a sphere. Satan made a choice to rebel against God. From the beginning Satan was a rebellious angel.
I had a dream about Satan as a child. I was in heaven when I saw God holding the hand of a small husky boy with a defiant look; both were in human form wearing clothes. I don't believe angels resemble humans, but Satan, as a fledgling angel, was portrayed that way in order that I, a human, would understand. God was leading the defiant boy into heaven. In another dream, God had just created an angel. It had the appearance of a brilliant cotton ball. God tossed the angel into heaven. The meaning was clear, the angel was free to roam heaven and do whatever it wanted. After a short while, the angel returned to be close to God. I believe this is important. God gave angels freewill, they could be with him for eternity, or they could go out on their own. Evidently, Satan decided to be independent of God.