I used the crumbs for the first 3-4 pieces in the blocks and then when the block grew too large I started using strings.
Although I'm not using her instructions for constructing the blocks, my inspiration is this quilt by Sandy Bonsib. I haven't decided for sure but I may substitute hearts for the star blocks since this will be a donation quilt for HeartStrings.
There's been some discussion on Stashbuster about crumb blocks not coming out the right size and Nancie posted that she makes a template to use to keep her blocks the right size. Since these blocks are going to be 9 inches (9.5 inches with seam allowances) my 9.5 inch ruler was perfect for this. As the blocks get close to the right size I can see at a glance where I need to add the last strip or two and even how wide I need them to be.