What sort of foundation for MMA?

How strong of a BJJ background should you have if you want to start MMA? Or doesn't it matter?

Also, what's the injury rate like in MMA, if training noncompetitively?

first question is absolutely subjective.

second is impossible to answer.

Most MMA schools will teach (no gi) BJJ as part of the curiculum (sp?). Having had BJJ experience is an adavntage but not a necessity.