In the center, I'd almost like to see it without any sashing before really deciding. Especially since the blocks are direct opposites of each other. I think it would look great without sashing.
Borders.... wellllll..... Unfortunately, I tend to be a bit further along before I'm totally decided on those.... It all depends on the middle, and what else the quilt may need to make it look great. I audition a bunch of idea until I finally settle on something.