if your top is done don't wash it before quilting/binding- only wash--if it is pre-washing the fabrics before making the quilts---if you do a search you will find hundreds of us use minkie all the time---it quilts up beautifully with a long arm. do check with your long-armer to see if she has experience with it & any particular instructions.
i have used batting in a number of minkie backed quilts- i don't particularly like ones with out batting- i generally use hobbs heirloom 80/20. but it's your choice- i have used poly batts a couple times with minkie backed quilts.
minkie makes wonderful backings- quilts up beautifully- only down side i know of is the cut edges shed (alot) until finished (i generally purchase exactly what i need so i don't have to do any cutting on it- i order it in 2 or 3 pieces if necessary & when it arrives i take the package outside to open it & shake it out really good before taking it into the house) other than that i've never had a problem with it- the first time we took some to a longarmer was 8 years ago & it turned out so wonderful-now it is often our backing of choice.