Regarding tension, here is an easy to understand and remember diagram
http://www.superiorthreads.com/educa...-tension-works
The lady at the shop was right, if you are seeing bobbin thread on the top that means your top tension is pulling the thread up to the top so it is too tight (Or your bobbin thread is too loose)
Regarding the Minkee, I had that SAME issue happen to me. I tried and tried to fix it but never could and opted for a different backing all together. In my quilt I was using polyester batting and cotton thread. After much research I never did get a difinitive answer. I got responses like, it is the nature of the beast that minkee will just do that sometimes, cotton doesn't play nice with minkee don't use cotton thread to batting needs to be denser. I tried switching needles going both larger and smaller and it made no difference and it looked horrible. So I ripped and got a new backing.
I am curious what kind of batting and thread were you using?