Love your top! I really love that you included the selvages in the border...I've never thought of doing that! Great idea. Regarding the back - personally I'd go with a cotton 108" wide backing or even a bed sheet (180 or 200 thread count). From what I've read here on QB, batik fabric can be difficult to quilt (I may be wrong on this though and it may only be hand quilting batiks that is difficult). Minky is wonderful, but hard to work with. Have you considered using a flannel back if you want "softness"? Just a thought...
Can't wait to see what you've chosen!