These are things that will be debated forever! So much of it comes down to personal preference. Except for a few rules. If some of the fabric has been prewashed, you should prewash the rest. Things that are prewashed will need to be ironed. If you like the bit of stiffness that the sizing provides on unwashed fabric, then you will need to starch the washed fabric. Then, again, it enters the area of what is best for you. If I am working with a new pattern, I like to cut the fabric for one block and make it. Then I can see if I like the pattern and the color combo. If my orphan block has deep colors (especially reds or indigo blue), I will soak it to see if it has any bleeding problems. Then I cut the whole thing out so I can assembly line sew. I do not prewash, but I lightly starch anything cut on a bias to assist in not stretching.