Re: Premade characters
I'm generally with the camp that pregens are awesome for Convention games where there's not enough time to make characters and then play the game - but time is usually one of PbPs strengths. Not saying it's not a mixed blessing, but the fact that people can sit down and work on it when they have time is generally the thing PbP does best.
BUT, there are certain games I can see pregens working well for. A few systems come to mind, but honestly it's more a type of game. I always liked them in Paranoia, because it meant they were not only kind of tied to the scenario, but all the little subplots and secret society missions and whatnot were... well, deliberately matched against each other. And that can work really well. I find it's important for most LARPs, too, even apart from time issues, unless it's a full campaign.
Now, Paranoia probably has an advantage in that you're not really supposed to get too attached to your character, but I could see that working well in any system. If you have a game where those kinds of connections are important, both between the players and from the players to the... not just the world, but the game, specifically? There's a lot of advantage in being able to make sure the group has specific abilities they might need, or to plan ahead for certain traits to come up and be interesting, that does not then require railroading the game to make sure these things happen.
So, yeah, I might be tempted to run a pregen there. But if you're going that way, they have to be really interesting and have a good variety. I really, really hate looking through a stack of 12 pregens for a game and finding out there's one woman, and she's the healer.
Which so happens.
It used to happen a lot. I do think people are getting better about that, though.
...I'm not sure it really helps much with players cycling, though. I mean, yes, if you have kind of an ensemble on-hand, then when you bring in someone new you don't have to go through the whole creation process with them before they can join. But you do still have to deal with either them taking over a character someone else has played, or sorting out the abandoned character and then getting to a good spot in the game for someone new to come in and adjusting everyone to working with someone new and... and... well, again. This is a place where time works in your favor already in PbP: You can be working with someone in PMs building their character for the two or three weeks real-time it takes to get to where they can join anyway.
So... yeah. Pregens in PbP? Not necessarily always a bad idea. But I don't think they solve what you're trying to solve.