I use Wonder Under to fuse the pieces down, then use a Buttonhole stitch with #12 Perle cotton (I use Presencia brand) and a sharp needle with an eye large enough to thread the Perle cotton through. If the design requires embroidery stitches, I will sometimes use floss for that. Felted wool will not ravel, so the Wonder Under is not necessary to prevent raveling, but I do like the extra stability it adds. I don't use knots, but weave all ends into the stitches on the back. I also add an extra layer of wool to the back of the project, so as to hide all stitches and add stability.
To prevent "rolling" of the stitches, I lock down every third stitch with a tiny backstitch in the background wool. Works like a charm.
I don't wash my projects, but then I've only done small candle mats. If I ever did decide to wash something, I would do it by hand with no agitation so that the stitches wouldn't get messed up. And, I would never put it in the dryer!!!
ckcowl, that is a wonderful quilt!