Welcome to the board, a good place for advice and help. Quilting "rules" are made to be broken. I have seen crazy quilts with sashing but have never seen one without backing unless it is waiting to be finished. Most crazy quilts are tied instead of quilted and sometimes don't have batting between the front and back. I'm sure you will gets lots of ideas on how to join the pieces. I don't have a good idea of what to do since the pieces have been signed on the back and I guess you want that to be visible. I'm looking forward to seeing what others have to say.