I found out how I could use the Promarkers:
An artist called Stephanie Wilkinson was asked for some advise and what she said is that to use those markers effectively, I should be able to choose a range of 8-10 markers from light to dark and also I should have a thick piece of paper I could use to test the colors on to see what the colors look like before actually using them , as it is safer to do so.
Another thing that she mentioned is that also, for the markers i would also need a bleed proof paper to use them on so that the colors wouldn't bleed through the paper. She also advised that i should go over the color twice to be able to make the color stand out and not make it see through and also said that I should experiment on overlaying the a color of the marker and see what it would look like.
One last thing that I would like to mention is that she advised also that overlaying the color on wet ink would give a much softer ink.
If I had researched this much earlier I would have been able to achieve a much better quality of my initial design and perhaps i could have even achieved a much better final fashion illustration.