I'm interested in this and I want to pull out an antagonist that I've had for awhile now but never actually got to use but I've got a few questions beforehand.

1. This is the big thing I'm sorta wondering, as a more antagonistic character would you be making up your own schemes and plans or would GMs be supplying them with things (contracts and stuff) to help push the plot. I'm happy with either but I just want to know before I get involved. 

2. Are characters expected to be at a similar power level or is it just "Don't be OP"? I'm assuming the power level can vary but I'd like to check anyway.