To reply to everyone on the fence:
World:
The world is sort of like our world. You know how something like Dick Tracy, or Sin City, is basically our world with little tweaks? Things are darker, dirtier, poorer. More punk/goth elements. Corporations are more sinister, more crime and violence. Cops are dirtier... hopefully this gets you going. I don't like to set it all in stone as the characters are the central part of any story; not the world. A world that is malleable can be tweaked to have a better story with the characters.
I do not really want to go into the details and history, especially about mages and supernatural elements. This is part of the wonder and appeal that is Mage. If necessary I will PM certain people if needed to get them on board, but it might be back and forth. I have let DoN in on it as he may cohost it with me. As I am in Canada and he is in the UK, two people running the show may be better than one. Also, I lack experience with this form of roleplay. Suffice to say, the world may really have some people struggling to wrap their heads around it.
Character creation:
No one will start a mage. Everyone will be a regular joe. You'll work in a movie store, a coffee shop, as an accountant, a clerk, a programmer. Regular lives. Law enforcement is fine, detective work, drug dealer (small time), deadbeat thug etc. Everyone will come from the same area of the world, or end up there (working overseas). We'll roleplay the rest. Most will get their asses handed to them in a fist fight with drunken frat boys. Some may have families, others are single. Whatever you want. People are encouraged to create people that will work well together. Sneaky characters that go off on their own are discouraged, as it will downplay roleplaying, and make story telling more difficult as you need to devote so much extra time to one persons wish to go out on their own. Evil people will be disallowed, as will characters that cannot work well in a group. Nothing worse than when someone wants to play a necromancer and someone is a paladin. Either one kills the other, or people don't roleplay their characters. Neither is good, although I much, much prefer people play their characters. If someone wants to occasionally play a villain, that will be allowed (in so much as I would normally be roleplaying that character... it will not be their character, they will just be roleplaying it).
I do require everyone flesh out their character as much as possible. Are they a coward? Are they a drug addict? Love of women, coffee, power? What kind of family do they have, background growing up? As much as you can to make them as real as possible. Did they have a major failing, or could not be what they wanted to?
Character goals:
At first, it'll be mundane goals. Get a raise, a new job, a girlfriend. Go the concert they've wanted, get out of a loveless marriage.
I do not want people roleplaying enemies, except for people that are strong roleplayers that want occasional appearances, and are fine with their character being slain. In fact that goes for everyone... no one will be killed out of hand, but rest assured you CAN be slain. No combat feels the same if you feel you can't be killed. As long as you play in character things should be interesting and go well.
Game Mechanics:
I'm brushing up on the rules currently, but these should not matter. They are background to story, a manner of getting things done. If you want to be perceptive, strong socially, charming, etc, then that's your character. You can make the character fit any game mechanics, so the mechanics themselves shouldn't be too important.
As roleplaying in the forum is done differently that what I'm accustomed, the game mechanics may even change if they're not working out well. Most roleplaying is done very back and forth, with the GM asking for roles, and the results of those roles determining future actions. I don't know if forum roleplaying can be done the same. My gut feeling says it will be far too slow, so prerolling will be important, or even if/than statements. Perhaps dice rolling will not work at all, and a free-form story telling will be needed.
So at first it will be some trial and error I think.