I like it as is, no sashing.

I would not sash it. It is quite beautiful as it is!

I like it as it is.

I would not put sashing on it. I like it the way it is. You can add several borkers quite effectively.

I like it as is no sashing and I to think black would be beautiful as a border with maybe the piano keys with all the colors of your quilt same width as what you used in your blocks along outside edge of border to help give you more length and width.It is going to be beautiful no matter what you do really like diamond effect.

I would put a narrow light strip between blocks, maybe 1", then the same light fabric for a wider border.

I think it would look great this way.

It sounds like everyone is on the "fence" with advice. I'd put a VERY small LIGHT color sashing between the blocks and then another small border all the way around to frame it. Then add additional larger borders until you have it the size you want it to be.
I love scrappy quilts and yours is no exception. It's BEAUTIFUL!!!

I'd use whatever size washing *looks* right between the blocks and then add multiple borders to enlarge it if need be.
Diana

I like it without a sashing , but if you must go with a thin sashing, no wider than the majority of the strip widths in the blocks.