I am new to papier mache and new to this forum, but, from the reading I have been doing, letting the piece dry thoroughly before painting (one layer = 2 days), then putting gesso (Podge) on it.  There is also an exterior Podge, but I haven't found it yet.  I use the shiny, clear one for my decoupage.I get mine from a hardware store the brand Demco.  you can sand with fine sandpaper if you wish and use 2 or more coats, sanding between coats.  Then you can paint.  Water-based Varathane or water-based varnish is recommended.  Wanna skip the paint part?  Put one coat of Podge and, before it dries, cut up little pieces of paper (wrapping paper, or any other colorful kind - or use plain colors, then cut out colors for details (eyes, etc.).  Then Podge over, sand, Podge, and varnish or varathane.  Hope this has been helpful
Sharon