Lol you realy need to reread your bible btw. cause mentionings of the devil/satan arnt including the entire story about his betrayal of God. Its not in there there are only references to it.
Another reference is that Satan was the angel known as Lucifer/ angel of light. 1 of the arcangels.
Also whats important is that Satan succeeded in seducing Adam&Eve but failed so with Christ. Think that element will be implanted in the story cause the basics for it are there.
As for 11 or 12 folowers id include all of the PGS, Kuchinashi Mio and Setsuna. You say they are Simeon but thats only half true since their main alliance would be with the Girls school members and Cruz is a member as Yamada.
Also that Setsuna send that other girl to aid him fighting Hatfield says enough.
To add to my defence of Adam Arclight in being Satan
wiki-Lucifer
-former
Archangel
-Lucifer/
Lightbearer
ArcLight
to another note among christianity those that do know the scriptures any reference to an angel of light automaticly is identified as Satan nothing else.