Hello:
You can buy fabric right here on QB. Most is from quilters, so they know if it is correct for quilts or not. I have received nice fabric from #1Piecemaker, top notch. I use rotary cutters and understand your frustration with automatic cutters. People powered ones are tough enough, but you are in control. Don't cut yourself now.
We usually cut fabric into strips then into pieces (squares). As you get more adventurous, you can add more tricks. Don't use the curtains for your first project. Someone mentioned washing the pieces, but be sure to do it in a pillow case or a mesh bag. Otherwise you'll get too many ravelings from the curtains. It is wise to GENTLY launder the 100% quilting fabric and iron it afterwards. This will ensure a good quilt when you're done. Good luck and happy quilting.