I wash and press new fabric as soon as I get it and starch just before cutting. I feel it cuts and sews more cleanly somehow. Regarding using different qualities or 'weights' of fabric in the same quilt, for me it would depend on how much wear it would get and how special it was. In an ideal world, the fabric should be the same weight and quality because the weaker fabric will show wear. I think maybe even the stronger fabric adjacent to it MAKES it wear more quickly if that makes sense; but as i said, 'in an ideal world' and sometimes rules are broken and no harm is done. :D