I have taken management positions but never over a group that I had belonged too. I think that's a disaster in the making. If you're too intimate (in a workplace sense, of course ;-)) with those you're managing, you'll have trouble dealing with the others' expectations. Some will view you as a jerk where they once viewed you as a friend. Others will expect favors from you because they have viewed you as a friend. Friends take care of friends, and, now that you're in a position to play favorites, you'll have that to deal with.

It's much easier to talk charge of a group where you don't know the players very well.

I don't envy your task ahead. Best of luck.