Without free will, we cannot be good. We can only be what we are compelled to be... essentially, God's robots.
You're getting very close to answering your own question.
Volition is not an imperfection.
Jesus Christ had volition (free will) and opted to perform the will of the Father.
Study the doctrine of the Hypostatic Union.
“Free will is a sort of imperfection, since, if what God would wish for all of us is to be good, then free will is a trait which could lead us astray.”
Well, if good is not possible without free will, then it’s not really an imperfection, even from that perspective. The imperfection only crops up when people, through free will, choose evil. Looking at it from the other perspective means that only robots are perfect, but robots can never love, never make sacrifices, and never do anything virtuous at all. So, they can’t be perfect, according to God’s standard.
“Is it possible that, “Satan” is just another word for the evil that people commit when they do use their free will?”
Well, not if you believe in the Bible. It’s pretty clear that Satan is a being as real as you or I, even though all the details of his story aren’t filled in. If you want to cast him as a personification of evil and not a real being, then you are flirting with gnosticism or something, but not Christianity.