I would not wash them until they are already quilted. There are risks associated with washing them first. Risks include having the edges fray, having the fabrics shrink and distort in different ways, and having the applique fabrics or embroidery thread bleed. Most of these risks can be handled if you are aware of them ahead of time. For example, hand wash with little agitation to avoid fraying; block each square immediately after it comes out of the water and allow to dry blocked; use Synthrapol in the wash water to help avoid dyes settling into background fabric, and/or use Synthrapol in the first one or more washes of the quilt to remove any dye bleeds. However, it is still safer to wait to wash until the blocks are already quilted into a quilt. Shrinkage distortion from pre-washing may or may not be fully recoverable; in other words, some distortion may not block out. Quilting will prevent distortion from shrinkage, and Synthrapol will prevent dye bleeds from settling.
I would not use Biz or Oxy-clean, much as I love those products. I would use RetroClean:
http://retroclean.com/