I am using masonite for a theater floor and wondered what is the best way to paint this flooring matte black?

My experience has shown that it's best to seal the flooring with a white paint specifically for that purpose, then to lay down a regular semi-gloss black, then to cover THAT with a matte finish. Sometimes, depending on the size of the floor, it's better to use the semi-gloss then just use a clear matte finish rather than the black matte finish.