Honestly, I think the blocks are great! It looks like a couple of them already have a lot of white in the outer edges, so I don't think a white sashing would do it justice. But I think I would choose a color (from those used in the quilt) to make solid blocks between your pieced ones. If you put a pieced block inbetween, your original blocks may get "lost". Putting the blocks on point with alternating solid blocks as previously mentioned sounds good. I like the very pale "lilac" used in the very upper right corner block.....it is used in the quilt, but not much, so it will be a good background. This is all just my opinion, for whatever it's worth. I would take all the blocks with me to the store and lay them out on lots of different fabrics to see what catches your eye. You will know when you see the right one!