Thanks for letting me know you're interested! I haven't completely worked out the details but I'll try to answer your questions.

I sort of imagined the powers of the magicians to be based on the manipulation of reality. Each magician would have a specialty that is unique and complex, but I don't think there are any established branches of magic. Also, every power needs to have a weakness, and a significant one, that keeps the characters a bit more human.

As for how they've gained their powers, I'm sort of letting the writer be responsible for the backstory. I mean, at one point in their lives they discover magic within themselves in some way and have to figure out where to go from there. I think it would be interesting to explore the origin of their powers throughout the story as, though their powers are varied, they all seem to stem from the same place. 

I want to keep the characters more on the human side than the god-like side. (Think Marvel vs. DC)

I hope I've answered your questions, but let me know if you have any suggestions.