Well I am going to take a stab at this question?
I am going to use a rule of thumb I use when I am not sure how much.
I would say 3 uards for background, are the blocksgoing to be scrappy or coordinated??? What size do you want to make the quilt?????
Let me know more information and I will try to help you!!! Okay send me a Pm.
Later Happy quilting!!!!!