What is the best material for a decoupage?

I plan to apply decals to the side of a cabinet I am working on. The cabinet has been painted with a higher gloss Behr paint. This paint was also used for bathroom walls, so it has a slick sheen about it. The decals were painted on white paper using acrylic paints. I want to make the decals appear glossier like stickers and apply them to the cabinet's sides using decoupage. Right now, I'd like to cover the paintings with a lacquer or clear layer. Then I'd cut out the pictures and then glue them to the side. Then, I'd like to go over the decals with another clear layer to have it stick well. What sort of materials should I be using? Can Elmer's glue be an appropriate paste material?