Wow Lobster!! First off welcome to the board I am really glad you have found us because based on this quilt and your avatar quilt you are one very, very talented quilter! I can't wait to see more of your pictures, especially a bigger one of your avatar (hint hint) . :D
I absolutely love what you have sketched out for your quilting. I would not carry the wave motif down to the beige triangles in the shell. What you have sketched is just perfect.
Your border idea of adding embellishments there sounds good too. Some other options for your border could be the traditional clamshell pattern or the traditional "wave" pattern. Because the border is so narrow at only 1.5" I think the clamshell might work a bit better.