I'd be worried about your fabric fading if you have skylights in there. Just get some natural daylight lights instead
I just added a 8' length of shop lighting in to my craft room and I love it. I don't know why I didn't push for it sooner. It is so much nicer than my old lights that's for sure! I can see now! My craft room is about the same size as the one you are getting and one length was good for me. It's 4 4' flourescent bulbs. It isn't the prettiest to look at but the light it gives off is fabulous. I know it sounds silly but I spent at least a half hour deciding what color temperature I wanted to put in there. I'm very happy with the one I got. It's 4100. For me that works. I felt it was easiest on my eyes and a good neutral-ish shade for looking at my fabric and whatnot.
About the 8' design wall... if you have any way to make it wider than that, I would do it. If you make a really large quilt, you will really wish you had a wider area.