Here are some tips for setting the stage for any PBP or Chat game; Create a nice, simple, concise set of behavioral boundaries for the game. Since many of your players will be hundreds, if not thousands of miles apart, sometimes people feel free to be discourteous. Make sure your players are aware (even though it seems obvious), that things said in character do not necessarily reflect a players' attitude or outlook. Seriously, I've witnessed game destroying temper flare-ups over role-play. Set boundaries.
Second; keep combats as short as possible. Unless you are a dynamic writer, combat gets old pretty quickly.
Additionally, before you start, you should...in your list of house rules, let players know the default damage track. The norm is non-lethal, but, for several of the PBP games I run, since they are grittier and more "realistic", lethal damage is the standard track. It requires a stunt to do non-lethal (unless they are using powers that are non-lethal by description). This is important, because there is a heck of a lot of difference in the behavior of a character who might get knocked unconscious vs. one who could be killed.
Third; be flexible. Players will find ways to approach problems or challenges in ways you do not expect. Unless you are laying down some serious railroad tracks, it's good to keep a stable of extra characters and locations in reserve for those moments when the PC's do something brilliant or baffling.
Fourth; be fairly generous with Hero Points. HP's are the mechanism for the pc's to overcome becoming lost in the plot (HP for inspiration), pull off that really cool maneuver (Feats and Stunts), triumph against overwhelming odds (surge) or just plain, not be nerfed (HP for re-roll). Since Power Point awards, are usually pretty low...Hero Point awards during play are a good way to promote feelings of accomplishment. One of the biggest gripes with "super-hero" games is they lack the big "I leveled up!" milestones of say...D&D. Hero Point awards are a good way...in game...to reward good play AND increase PC effectiveness. Encourage their use and your players will find themselves happily finding new and creative ways to make their character more effective without you having to buff them up too quickly.
Five; don't fall in love with your villains. At the end of the adventure the pc's should triumph. If the villain is supposed to escape, have it happen sooner than later. If the villain is supposed to fight it out to the bitter end, then they should be beatable. (Ablative Defenses and the "5 shot" Unreliable are great for making villains that start incredibly tough, but, get worn down and eventually beaten by tenacious pc's)
That's all I've got time for at the moment. I hope this helps. Have a great game!