According to Revelation 12, the rebel host aggregated one-third of the angels in heaven. They fell for 9 days. Their number was estimated in the 15th century to have been 133,306,668 (the tabulation of Cardinal Bishop of Tusculum).
There is ANOTHER story based on 1 Enoch (a Hebrew book that did not find its way into the Old Testament), wherein there was once an order of angels known as The Watchers. It was their job to watch over the affairs of men - the key words being "watch over". No meddling, no touching, no direct contact - just watching.
Bad move as per this recount:
"And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them, that the Sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose. . ." (-- Genesis 6:1-2)

The Watchers not only came to earth and mated with human females, they also instructed them in the forbidden and arcane arts of botany, astrology, and astronomy. Further, they showed them how to make magic and weapons, and how to use cosmetics. God was not a happy camper at this point!
His displeasure increased considerably when the offspring of these matings were born into the world. They turned out not to be angels, but monsters who became great giants that killed and ate any unlucky humans that they caught. And should there be no humans about, they killed and ate each other.
God enlisted Archangel Michael to round up the fallen angels while God wiped out the giants. Michael imprisoned these fallen angels in the valleys of the Earth where they stay until the time came for them to be hurled into the everlasting fire. Thus according to the information stitched together from Genesis and Enoch, it was these underground angels that would comprise Lucifer's rebel army.

There are many other accounts of the way in which Lucifer and the other "fallen angels" met their fate, how many there were, their ages, how long they would live. But despite the best reckonings of philosophers and others, these answers remain elusive.
Also; almost everyone has a dream of falling, only to wake with a shock to their system.
Some people fall harder than others. Apparently the bigger they are the harder they fall ?

Coloured painting by Anne Sudworth
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