Definitely it needs to be quilted to stabilize it and also enhance the wonderful work you've done. It is magnificent!! Generally quilting would use skin tone threads where suitable to create dimension to the face, in other area such as the hair suitable colors of threads could be used or perhaps a dark monofilament thread (one with low sheen). For the shirt the same method of quilting can be applied..serving to enhance but in no way diminish your work.
If this is your first quilt goodness only knows what your quilting future holds! Your are an artist with the patience of a saint. Thank you for sharing. Please consider showing this piece of art once it's been quilted. People will so enjoy seeing your labor of love.
I remember seeing a quilt of the Last Supper done by a gentleman..it was totally awesome, it also had an unbelievable numbers of tiny squares!!