You should also consider that different sorts of games will require different amounts of GM input. A typical D&D-esque system game might require a GM post after every single player post, to resolve the results of that player's action. A more freeform game might have days and days of posts go by where the PCs are acting among themselves, having conversations and resolving things without the need for your input. There are tradeoffs between the styles, though, and if you're the sort of GM who doesn't want the players improvising details of the world, moving around the NPC's, etc. then that sort of hands-off approach probably isn't for you.
And as others have said, just be up front with your prospective players when you're recruiting so that expectations are matched.