First a few question for you. Are you spraying with a gun or rattle can? Are the graphics going to be paint or vinyl? What kind of paint are you going to use "ie base clear, acrylic enamel, lacquer"? The below advice is based on spraying with a gun and painting the graphics with a base clear system.
so the easiest way to get a smooth transition between the two is to paint your base color then lay down your graphics then apply three coats of clear. Then you need to wet sand around the graphics lines or the whole body depending on the orange peel or debris in the clear. After that lay down 3 more coats of clear and the lines should be gone then.
Now about the flat look you are after. If you are spraying with a gun you can add flattener to your clear and this will remove the gloss, the more you add the flatter it gets but make sure you follow the directions for mix ratios.
As always these are just my personal opinions and others will have their own
