i disagree with your google thing. because i prewash everything. that's just what the "rule" was when i started quilting in 80's. i prewash minky. i also prewash the blocks of scrap quilts because much of the fabric scraps i'm given are not prewashed. i fill tub, swish by hand gently, drain & spin dry. i use at least 6 color catcher sheets because usually number of blocks are for full size or larger quilt. i then press the washed blocks before i set together. one time i didn't do as above and after quilt finished ..washed and one square was wonkey. i got the remains of a fabric that was in the block and measured it before & after washing. the shrinkage was about 3/8 inch side to side for one of the blocks' fabrics. now for the minkie ..yes it's poly, and i still prewash it for quilts. and after i made a bed for my kitty with unwashed minkie and it shrank big time ..i'm glad i prewash the minkie.
for quilting minky i use no special thread. i like to see the quilting thread on surface ..just like it shows in vintage/antique quilts. i use lighter thread in bobbin tho. both weights sink right in to most minky and aren't readily visible. i spray baste all my minky & flannel backed quilts. i use to pin, then i use to thread baste ..regardless of how careful i was fmq on my domestic i would get a few tucks/pleats in back. i tried spray basting a few years ago and it was perfect. the back was smooth w/o mistakes. i live far enough north that opening windows for spray fumes odor is not practicle. i use the odorless spray by dritz and it holds well, not stickey. and i can breath. joanne's carries it.