What medium should i use for my painting?

I've got an exhibition coming up, my first one infact, in a few months, for which i need to create a piece on identity. I shant go into too much detail but it's going to look pretty grim, i need to show a ravaged human, lots of blood and decay etc, so a very mobid feel to it overall. I want it to be high in fine detail in certain areas, as that's what i'm good at, though not nessacarily everywhere. I want it to look realistic, not abstract or cartoony etc, but want to have a stark contrast between light and dark. So what do you suggest i use? I have already considered inks, as they would be fantastic for fine detail, and have briefly considered gouache, but have never used it before and do not know how it turns out. I hear is it really thick, but not good for multiple layers. I like the idea of a rough, choppy feel with rich colours but i would feel more comfortable being able to paint over mistakes etc so the layers are a problem. I just need it pretty dark and disturbing - What do you think i should use? All help is majorly appreciated, thankyou <3