When doing a flat paint job, forget about allot of what you know about a shiny paint job.
First off, you can use black primer as your base coat. It will not be your finish coat.
Get yourself a couple of liters, (quarts) of Duplicolor Matte Clearcoat.
It is a laquer. Easy to apply, easy to fix. Spray it on in light coats. You can re-coat fairly quickly. The lacquer simply has to set up which it does in 1/2 hour or less.
Now if you want a heavier paint job, use your black primer and cover in Duplicolor Jet Black first. Then use the Matte clear coat the same way. I did mine this way, but, I cheated on a couple of spots and you can't tell the difference.
I call it the "Batmobile" now.