My sewing area is in the basement as well. I love it. It used to be our family room but now it's mine. There's a sitting area, a bathroom, and lots of space for my quilting stuff. I have 2 windows below grade but they really seem to flood the area with light during the day. I also have lots of lights around the room. I hung some of my quilts to make it feel a little more homey. I have carpet on the floor (because it was a family room). I really haven't noticed much difference in the temperature or humidity. Here's a link to my pictures if you want to see it.
http://www.quiltingboard.com/members...albums878.html