Thats enough to start- I don't think you *need* anything else. Mic cables and stands, of course.
Dig in, man! Have fun. The "getting started with Mbox" guide is the place to start.
At this point your skills are more important than the stuff you're using. Use what you have until you know what it can and can't do- THEN start looking around for stuff that will fill in the gaps. By then you'll have a much better idea of what you need and why and you'll spend your money better.
Have fun!
Chris