I think your idea is a good one, and some people might put bits of this info in when they PM newbies. The only thing I would be wary of, is about giving too much information in one go. That can make things even more overwhelming. I have two thoughts.
One is that perhaps basics should be covered first - the stuff you really need to know before posting (about trig warnings and very general stuff about the commonly used forums) and then after a week or two, then send on more information. Sort of a hi and welcome and that you're open to questions, and then a 'now you're settled in' type of thing. Just so there isn't so much to digest in one go.
The other is to have a welcome, but refer to threads that might be of interest, such as dragonfly's post on usergroups, more detailed information on the different boards (which I don't know that this exists, but it needs to), things about the busses, how to select or submit an avatar, things about signatures, the post about the welcome cows. If they're as links, people can check them out as they need, and aren't so bombarded with info as if it was all in one chunk.
Just more ideas... I think dicussion is good Kate. Good thread
