Hi David ,Jump in and try the portrait,get your feet wet so to speak!I've seen protraits thin and thick and lately i've grown to love the look of the thick ones.Your probable right about personal taste though.I've heard it said that black felt rings out the beauty of the project. anything can be used as a backer.Try holding the portrait up to different colored things in your house to get an idea what color will enhance it best.the walls the fridge,the carpet,chairs tables just get a quick idea what to strive for.Colored craft paper aluminum foil ,i like poster colored thick paper my self ,cheap too..Maybe even a picture of flowers if it's a female portrait.Your the artist and every one has their own signature in their work .Enjoy what you do an d most of all have fun doing it!