If you want to be able to hang up the board, you should attach a fastening to its back before you start to decorate it (you might damage the 3D/raised parts by adding on a fastening or hook after the picture has been finished). Measure and mark out a rectangle inside the board to show where the magnetic part will be. Paint this rectangle with two coats of the magnetic paint. With the texture effect/modeling paste and a simple flat paintbrush, paint on '3D-look' clouds at the top of the picture. Try for this 3D effect at the bottom of the picture as well, especially along the sides.