I think batiks hold up well to washing so using them shouldn't be a problem. They might fade some, but that will only add to their charm. I agree that having a design wall/flannel backed tablecloth to play with them on is going to be very helpful in planning for using the blocks. I would also not make any strip blocks until after using up the pre-made blocks as you might need the scraps for sashing, etc. in setting them. Also, there is nothing that says you can't use non-batiks for setting these blocks! Some of them would look great with some tone on tone white or other light colors between the blocks.