Do you have a picture of the minky, is it a really fluffy one or something a little more velor like?
most minky is 100% poly so you won't need to prewash (but I always prewashs everything because I"m just that kinda person). Though because it won't shrink with the rest of the quilt, I would suggest prewashing the other fabrics.
It's also really streatchy so if you're planning on quilting it, make sure you baste really really well... or better yet, use a basting spray.
As far as to use batting or not, it's a matter of how thick you want the quilt. if you want it heavier then add batting. The minky with cotton top will give you a nice medium (kinda on the lighter side) weight baby quilt.
Your walking foot should be just fine. i've only used minky with the minky side on top. I'm not quite sure how it will go through your machine with the minky side down.
I hope some of this helped