Wow-those are beautiful blocks. I'm no expert but I wonder if sashing and cornerstone blocks would be too busy?? It would divide up the quilt too much I think and detract from the flow of the different blocks. I love your color choices and the cream setting triangles would finish it off nicely. I like how the eye just flows from one block to the other.
There are much more knowledgeable (sp?) people on this board who can probably give you better advice.
I really love what you've done. Good luck with whatever you chose and please post a pic when done.