Having ran a few games on E before my time to GM dropped, I have some good experience with it. Things can roll out pretty much how you want them to. No matter what game play will be slower then table top, but this leads to added detail you might not otherwise have. As in anything forum based the reliability of players and GM greatly effects all factors. Aside from this, there are plenty of tips and tricks to making things roll out smoother. I'll list some that I use, and some that I didn't like but plenty of other GMs have lubriciously effective results with.
Pace well. Make sure players post at-least once a day if at all possible. You might want to skip their turns or npc them in battle if they slow things too much there. Roll everyone's initiative before the battles start so there isn't any fuss with it. You just tell them the order in the initial scene. Otherwise you can omit initiative entirely, simply roll for the enemies and for the players and the party that had the highest roll goes first in the order of who posts the fastest. I didn't like that approach myself, but many swear by it.
Attacks of oppurtunity should probably be handled by the gm for ease of use, over-viewing it and simply having the player play it out on their next turn. This is of course saying the player doesn't know he's provoking one, and already posting it. Let the players feel free to roll checks in their posts without running them by you first. Just make sure you check their rolls, and if it requires a different skill just review their sheet and post it in. I'd recommend either E's dicebot, great since the rolls are logged, or Invisible castle. The latter is much more user friendly, but harder to verify if the players just rolled till they got what they wanted to see.
Another point to keep in mind is having a good Sheet generator. I'd recommend mythweavers for 3.5, though plothooks is pretty decent too. You should throw out lots of story XP, ad hoc experience can be a big aid here. Accomplishments earn however much XP they impressed you with, and good roleplaying nets a lot too. Likewise, you can just have them raise a sudden level whenever you think they should. I prefer the former, but many here use the latter to great results.
Last but not least, you should get a Map generator. I use AutoRealm myself, but there are a few easier to use ones out there. At first the maps may not seem necessary, but you can notice that confusion easily runs abound when people can't see what square they are in, and how many leads to their ally or enemy. In short, grid style combat is easier to manage with an actual grid.
If anything else comes to mind I'll be sure to add it. Till then, good luck with the game.