How do I currently contact new online students at beginning of semester?
At the beginning of the semester, send out a "Welcome to the Class" email as a News forum post one week prior to the start of class. That email contains general information about MCMoodle and the course, and includes attachments and links.
On the first day of class, send out a "Start of Class" email with more detailed information about the course. On that first class day also request that students post to the "Introduce Yourself" forum.