I'm really behind on my prewashing but I think it's the way to go. I don't have any reactions to chemicals in fabric now but I know that stuff can build up over time and make you BECOME sensitive to things, so I try to handle unwashed fabric as little as possible so hopefully I won't ever suffer that.
I use gentle cycle but I don't pre-sew or pink my edges. I did some experimenting and I think I lose about the same amount of fabric whether I "eat" it up pinking or pre-sewing or I let it fray off; and to me the work of snipping the frayed strings is about equal to the work of pre-sewing or pinking so I just toss it in as-is and use gentle cycle and that works out fine for me.
When I dry my fabric, I set my dryer to damp-dry (it has a setting for that, love it) and drape the fabric over a collapsible drying rack to finish drying. That keeps it pretty flat so I can just fold it a couple times and wrap it onto one of my comic book boards without doing any pressing. I save the pressing for when I'm about to cut the fabric.