Ok i havent used the Createx black, but i think it should be a color that covers up pretty well. If you havent over reduced it too much it should be black, at least when you put some more paint on the paper. My pick is that its the paper that wont show
the black as dark as it should be. You can try to put some more layers of black on the paper and then see how it turns out, or try a different paper. I only use printer paper for excersices, and when i wanna paint something i use airbrush paper.
There are several out there, i find a very good one is the Harder and Steenbeck airbrush papers. For the thinning i dont know how thick the paint is since i havent used it yet, i guess other people can help you more here with that. I would suggest
that you try out to put in 4 drops of paint and then 1 drop of reducer and see how your gun sprays, if its not so good add one more drop and so on till you have a good spray pattern.