I'm slightly confused with the material assets. I'd love to be able to add a metallic component. I suppose I'm only more familiar with standard unity shader code. When I try to add a map, it says that term doesn't exist int he code, but I can't figure out how to modify the code or see what existing variables are availble to me.

Thanks for the help, this is so amazing and I'm jumping in joy :)

For a better sense of what's available to you, definitely check out the files in Raymarching Toolkit/Assets/Shaders -- the .shader file there and the .cginc include files are what is used to generate the final shader.  If you have any ideas on how to make things you're trying to accomplish easier or more transparent, I'm all ears! :)