Don't second guess yourself on that fabric. .... It's beautiful!!
In particular, I like how it is dark, yet bright and cheery.
I love how there are those sun spots showing through in the flowers.
Yes to the black ... for good definition from the prints to the sashings.
I agree ... hold off on your outer border decision(s) til you get the centre put together.
My only extra thought, and I hope I do not muddy your thoughts ... if so, just ignore ....
Not being able to see the print IRL, it's hard to know for sure the true colours.
Are the blacks/darks in the print truly black? or are they a black/navy? or black/purple?
Maybe audition those with it to see which "tone" of black you want for it.
It shows that sometimes simplicity creates the stunner and not always intricate piecing!!