Trying to get the picture. You have three butterflies that you are appliqueing to a background, using fusible web .. and you will then stitch the edges down? (around the fusing)
and, you want to embellish the butterflies with embroidery (by hand?) ... if it is simply thread embroidery, you can do it as soon as you have the butterflies attached to your background.
Have you invested in a teflon sheet?
I didn't see that you mentioned how many blocks you will be making, but you will want to iron the blocks as you join them. Since the iron will be hot, a teflon sheet placed over the top of the embroidery and fusing should protect the embroidery.
Is that a better answer for your question? <wave>