No window means you can store your fabric without worrying about fading. No window means more space for a big design wall and floor to ceiling shelving units. I would move the sofa to the short wall where you currently have your sewing chair. This would give you the L shaped section of the room to make your own. A nice shelving unit with doors will store your fabric and supplies. Make sure you get one with handles that you can put a cupboard lock though to keep the kiddos out of your tools and stuff. The top of the unit can hold quilt batts on top of it. More of the foam mats mounted into the wall alcove would make a design wall that you could pin into. Use the double stick command strips or sticky Velcro strips if you don't want it to be permanent.