I would never have thought to doing mosaic and decoupage in one project. Love the idea and of course it is going to be one of my projects too. Many years ago we did decoupage, still have a couple of my mom's pieces. I'm really excited about doing this now.
I even thought about using decoupage on a BB.
Debbie, you asked about using fabric. My mom used to use Elmer's glue on her material which stiffens it then you can cut the pieces out. It surely would work on decoupage. Just brush the glue all over your fabric, let it dry and then cut out to your heart's content.