Really? Maybe it's more a matter of you not asking any of those questions in your OP to which I responded.
You simply stated you were confused about the role of the Holy Spirit and the angels.
I'm not confused about such matters any more than I am confused about the role of the Lord Jesus and the Church. One is God the other are servants and you understood that yourself.
It seems to me you are simply confused about the role and place of angels within creation based on your other questions and God's dealings with them.
Maybe God doesn't want you to know but deliberately keeps some things hidden so we learn to mind our own business and not poke our noses into places they are not welcome.
But as to your other questions.
Angels and Demons (although technically that is a misnomer as it is a description of their purpose, ie. messengers not what they are ie. spirits) were created before the world was laid.
Job 38:4-7
“Where were you when I laid the foundations of the earth?
Tell Me, if you have understanding.
5 Who determined its measurements?
Surely you know!
Or who stretched the line upon it?
6 To what were its foundations fastened?
Or who laid its cornerstone,
7 When the morning stars sang together,
And all the sons of God shouted for joy?
As I said, there purpose is in the name, they are messengers, servants of God. They do whatever He assigns them to do.
As to being needed? Is man needed or wanted?
Seeing as two thirds got kicked out of heaven and Satan is called a murderer and a liar, I think it obvious they can sin.
The lake of fire was created for the fallen angels Matt.25:41 so unless you hold a Reformed view that says God created certain beings just so He can "flex His muscles" and destroy them it would seem to me, knowing the just and loving God that He is, there would have been some sort of period given for repentance. Afterall, the Lord has been known to overlook ignorance. Acts 17:30
Doesn't say they are superior, it says they are greater, stronger and more powerful. The President is greater than you, there are men stronger and more powerful than me. Neither case makes them superior in the sense of being better. If that is what you think 2Pet.2:11 is saying, then I think you are mistaken.
Where are they called mediators?
You don't get a dog and bark yourself. A purposeless life is no life. God knows He cannot create life and then give it no purpose. Without purpose, spirits and man alike, would drown in hopelessness.
Considering man was made just a little lower than the angels, I believe we can look to God's purpose and His dealings with us and get a reasonable glimpse of His purpose and dealings with spirits to understand how it works. As to any specifics? If the Lord wants you to know, go ask and it shall be answered, unless it's His secret for now.