If you want to use inks for shading, just water down your inks and be careful when you apply. I find the best technique is to do several 'glazes', watered down ink on the area which, on the first glaze, doesn't show up much at all. But you build it up, and you are able to stop when you want, achieving a shading effect if you want to. Afterwards, you could also just paint a small amount of the ink itself into the deepest area, i.e, a the area where the banding meets the armour on a SM shoulder pad. This will further deepen the shading.
Also,
www.coolminiornot.com have loads of really good articles on all aspects of painting. It's definetly worth a look at.