Seems to me you are mixing media which is why you are having trouble. I would go with the plaster strips......they are the easiest, and dry very quickly. Once it is dry, you can do anything to it...paint it...collage on it....glue "baubbles" on it...or whatever.
I would not put plaster over papier mache or celluclay (which is just paper pulp mixed with a cellulose glue) on top of plaster. You can use celluclay over papier mache (since they are pretty much the same thing).
I would not worry about the pores on the the plaster strips....the more you work with the strips, the plaster starts to fill in the holes. Also, you could use a brown was on them and it will look old....and you could use silhouette shapes on them...that would be kind of cool. Also if you paint the paris craft strips with gesso or even acrylic paint, it really fills out.....You could also cover with tissue paper collage...that would look nice.