My feeling is always, "do whatever works for you." If it ends up looking fine, then you did it right.
As for me, I don't use a 6" overhang on the back, but do make it about 3" which I sometimes trim so that I can turn it over slightly and hand sew. I don't find that complicated, and the hand sewing doesn't take me all that long to do. It ends up looking smooth. When I quilt in sections, my strips usually include sashing and cornerstones which help me match the blocks to keep everything square. I generally add the outside borders after putting the blocks together.