Beautiful star!

As for borders, I really like a simple border on this. I think something like a piano key border might be a little too "busy" and might detract from the beauty of the star. Personally I like one thin border on the inside, maybe one inch wide, then a slightly wider outer border 2-2.5" border. Either use colors from the quilt or pick other complementary colors.

I'm sure it will look great whatever you decide!