Yes to having a textbox to enter custom crosspost footer text in. Yes to an explanation of how to insert the crosspost code in a custom style.

No to the rest of it. I've made crosspost info invisible in my style and I like it like that. I don't want dw inserting anything in my entries automatically, and I don't want other users inserting any kind of footer or sig line in their entries automatically. If they do, they should at least have the trouble of setting up an external client to do it.