If you buy Minky, remember that you really shouldn't seam it, so it's only useful for lap size quilts. Just buy enough for the length of the quilt you will be making, plus 8". I usually buy 88" when I don't have a specific quilt in mind.
Flannel also makes a relatively inexpensive, good backing. I usually buy 8 yards, and shrink it first.
Have fun! It looks like you are in fabric heaven.