I don't understand please explain a few things

Did my best to follow this movie but things still escape me and hopefully someone can discover the answer.

1) Parnassus said he started as a young monk, so are we to believe that many years ago people had the ability to use magic? (floating carpets)

2) Was Parnassus a human to begin with or a mystical being with powers? And if so, why are the humans now without such power?

3) Why did the Devil pick only Parnassus and not anyone else? Were they originally friends?

4) Where is Anton's story in this? Was he also just picked up to forever join the show? Was he first a human like Tony or something from the past like the Dwarf and Parnassus?

5) How did the magic mirror come to be? Why is Parnassus the only one that can activate it with meditation?

6) Why does Tony turn into different faces every time he enters the Imaginarium? Is it because he is slowly accepting the fact that he is lying to himself and everyone else?

7) When they stop suddenly in the rain and discover Tony's body coincidentlly hanging from the bridge below them, was it luck, destiny or did the Devil have something to do with that?

8) The Devil mentioned he tried getting Tony for a while but just couldn't do it. That even the mob would most likely not tear him to pieces because they will be charmed by him. He mentions that Tony has scars or horns on his forehead. What does this mean?

9) I notice the devil almost never confronts Tony except when he morphs into a snake and is upset that Tony saved a soul. Tony didn't look shocked and appeared to recognize the Devil. Did he once make a deal with him and had to find some way to get into Heaven to escape him? Maybe that's why he got into the "charity" business to have an appearance of doing good in the eyes of God?

10) Is the old man God himself? Do they constantly make bets with each other at the expense of other people's lives as an eternal hobby out of boredom? At the end the Devil gave a nod to Parnassus and he returned the gesture. Is this why Parnassus didn't just go ahead and scold the Devil, because it's all part of their game?

Right now that is all I can think of, if anyone has read the book ( if there is one), I would appreciate it much if you could explain my questions. Thank you very much for your time!