I was a wedding dress designer and dressmaker before I quilted, you normally match your seams and sew with a straight stitch on a 5/8 inch seam on a garment and then overlock/serge to finish off. Because a serger moves so fast and cuts at the same time, the pull of the feed dogs creates the mismatch of the two layers if not already stitched together. I would mismatch my seams deliberately and make it a 'design feature'. As you are going to back with minky and this is your first quilt, I would use the birthing method to attach the backing, which you could use your serger for. Good luck I am sure it will be soft cuddly and a much loved quilt xxx