THe clear with flattener in it is not as "flat" as mine. Mine is like a chalkboard, it looks like it would feel like velvet, however it is smooth.
We did mine first as roachie said, and it was semi-gloss. Looked good, but not as flat as I wanted.
Sanded it back down an got the PPG that's on it now. I was going to do primer, but didn't want to put that much into it, then have it loook bad in a few months. Primer would be sweet for a older truck, but yours is too nice to just do primer. If it doesn't have to be as flat as mine, do it semi-gloss like roachie said. I think it would hold up much better. Mine is a pain in the butt, if your hand is dusty, you can leave a handprint on the side of my truck. It doesn't wash off, kinda has to "wear" off. Very similar to a chalkboard. When it's wet, it shines like a BC/CC paint job, when it dries, it's flat. Same with the mud streaks, etc.