I've never done any roleplaying outside the forum, so I can't speak for real world games, but when it comes to forum RPs... Here's the thing. In a real world game, when you ask the GM a question, you get a response straight away. In a forum RP, you could be waiting for days if the GMs busy.
As a result, player pretty much have to DM minor interactions on their own to save time and keep things interesting. Players will sometimes roleplay both sides of a conversation until they reach a bit that they can't know the response to. You'll also find that players have to post what looks like an incoherent barrage of questions, only to then have the GM respond as though an actual conversation had taken place.
Three rounds rapid is definitely an effective way to handle fights and such, but perhaps the best advise I'd have is that, as a GM, you'll probably have to retcon events occasionally. Sometimes it's for something minor, like reordering posts into an actual conversation, sometimes it's something bigger, like outright declaring that a players post is non canon because something happened that renders it invalid.
Of course in the end, if a game play mechanic doesn't work, you can always change the rules to something that does.
