Wow! That's a great quilt, especially for a first! You must be a "natural" at this!
I also like to see a bit of the original fabric on stack-n-whacks. If not on the front, then do a panel of it on the back. It's sort of a childish thing to do I guess but I have fun tracking down where each triangle came from in the original fabric pattern.
I like the idea of a "night sky" border. Dark blue with random dot-stars would be perfect.