For these quilts I used only one layer of Hobbs Heirloom batting, without a thin layer of cotton batting (typically Quilter's Dream Angel Request) functioned like a backing, like what I have done in my other mini quilts. It's easier to quilt, but I think an extra layer of cotton batting does improve the dimensional texture and enhance the stitching details. I should not make shortcuts next time.
I quilted with Superior Thread Bottom Line purchase a few years ago. I found it not as smooth as WonderFil DecoBob. Bottom Line is a matte thread, blending into the fabric quite well but lacking the sheen of DecoBob. I think it can be a good choice for modern, neutral quilts, but the quilting experience is not as enjoyable as matte threads generally have more friction when free motion quilting. I also found when a thread blends so well into the fabric, it can be very difficult to see the stitches while quilting!
Just filling in the background with various types of motifs is lots of fun! No markings and no really planning ahead, I simply enjoyed that zen of free motion. It's relaxing and calming.
I love these panels and they are already on the wall... Christmas is coming... eventually!