I'd cover the whole thing with a few light coats, it seals in everything beautifully and gives a nice surface for not only decals, but washes and filters. It also keeps the surface consistent that way. After filters, etc if you use them, you can hit it with some dry pigments to knock down any surviving shine. Some people dull coat it afterwards, but that can get hazy if too heavy and will change the way the light reflects, therefore it'll change the color too. If you absolutely have too spray a dull coat, you'd be better off misting it from a distance with a sandy color, but honestly, just driving the thing outside works too.

Spray it straight at around 12-15 PSI. Windex is it's favored solvent when you clean up.

These are all covered with a lot of Future, no visible shine afterwards...