There are some great Crazy quilt block patterns if you want to make a easy pieced block and then decorate it with embroidery stitches. If you want to use random scraps, you can do that on foundation of some kind or not, completely up to you. The benefit of using a foundation is the blocks usually lay flatter and you have a size to cover. Antique crazy quilts were not usually done in block form but worked as a whole top. Find a method you will enjoy and go for it!