My wife and I have pondered this many times. Yes, of course, angels have free will, else they would not have been able to revolt or rebel. I believe God created the angels, and then at some point later created this universe. Lucifer and his rebels saw how pleased God was with his creation and became envious (this was their temptation), Lucifer selfishly thinking he knew better, started a war in heaven. At the time, Lucifer must not have understood the complete power God had and has, and thought He could be defeated. After getting kicked out, these fallen ones were left with trying to corrupt and destroy this creation.
We know Satan deceived Eve; fallen angels(sons of God) took human form and impregnated human women before the Flood which caused the "mighty men of renown" to be born, ushering in the horrendous violence and evil which caused God to destroy all of them with the Flood; these fallen angels are probably the ones mentioned in Jude, as gonefishing quoted; Satan still had to report to God as to what he was doing and thought he could make God wrong about Job; Michael the archangel contended with Satan over Moses' body; angels took human form and partook food with Abraham, and then also with Lot in Sodom, so we know for certain they could appear in human form.
Could it happen again? Yes I think so, although the loyal angels now have a great reason to remain loyal, after seeing what transpired with the fallen ones.