This is true, I'm not too worried about the monotone as the image I want is all black lines, and as I'm making the image larger across my chest I think this will create more negative space between the lines, however I will mention the overcrowding of lines and the possibility of it bleeding out into a big blob to him when I meet him in person tomorrow.
Any other pearls of wisdom I should ask him about would be warmly welcomed!
What you need to do is some research. Find a reputable artist, experienced with coverups and see what they can do. Get multiple recommendations from people with good work.
Did you not look at what they were going to tattoo on you before they started????